Since you have memorized the hand positions and mastered neutral-position techniques, I will now teach you left-hand techniques. Due to the limited time, we can't cover all the left-hand techniques, so I will introduce only the basic techniques in this and the following lesson. 
First, I will teach you how to raise or lower the pitch to play the basic intervals on the Dan Bau, such as major second, minor third, and perfect fourth. These intervals will serve as the basis for finding all the other intervals. These are the most common intervals when playing the Dan Bau, which originated from the scales used in traditional Vietnamese folk music.
Remember, because of the character of the rod and the string when raising the pitch from the neutral position, we should not bend outward too hard - a fourth is an upper limit.
For example:
G A B C
Certain pieces require us to go up to a fifth, but this is very rare.
G A B C D
Because if you bend the rod too much, you might break it or break the string. When bending the rod inward from the neutral position, we can play larger intervals. For example, we can reach a fifth or even a tenth down.
G F E D C B A G F E D

First, I will show you the technique for bending inward and outward to major second (M2). Bending outward means bending the rod to the left (from the player's perspective), to increase the pitch and reach higher notes. When bending outward, use your fingers to bend the rod to the left. Keep your thumb on your index finger, like this: The wrist stays in line with the forearm, forming almost a 90-degree angle with the upper arm. Use the fingers and the arm to bend the rod to the left to reach the note you want. From the six nodes of the Dan Bau, we will get the following notes by bending outward to the major second (M2):

Bending inward or loosening the string gives us a lower pitch from the initial note. In contrast to bending outward, when bending inward, we use the index, the middle, and the ring finger along with the arm to bend the rod to the right. The thumb can be relaxed instead of staying in the original position.
From the six nodes, bending inward to major second (M2) will get us the following notes:
C - Bb (I - first position); G - F (II - second position); C - Bb (III - third position); E - D (IV - fourth position); G - F (V - fifth position); C - Bb (VI - Sixth position); 
Bb (I - first position); F (II - second position); Bb (III - third position); D (IV - fourth position); F (V - fifth position); Bb (VI - sixth position) 
Remember, when playing this technique, as you lower or raise the pitch, you must pluck the string and move the rod at the same time, or else you will get indistinct notes. For example, playing correctly in this technique will sound like this: (Playing)
If you either pluck the string first or bend the rod first, you will produce this kind of sound:
Once you played the note you want, and you want the sound to end, use your right hand to stop the string from vibrating to really finish the sound before guiding the rod back to its neutral position.

-     Correctly play the major seconds up and down.

-     Place your left arm at the 90-degree angle to the rod, keep the wrist straight.

-     Pluck the string with the right hand and bend the rod with the left hand at the same time.

-     Control how much you are bending the rod to find the accurate notes.

 

-     Produce notes that are in the correct pitch and at a volume and quality similar to that of notes in the neutral position.

-     Produce clear sounds that are separated (non-legato) from notes in the neutral position, avoid unclear, murky transitions.

 

-     Practice each interval until you can bend the rod in a precise and quick manner to produce the desired notes.

-     Practice bending outward (raising the pitch) to major second up first, then bending inward (lowering the pitch) to major second down. Once you have a good grasp of these two techniques, practice opposite bending, meaning going straight between bending outward to bending inward, or from bending inward to bending outward, spanning a major third in total. For example, going from D to B-flat or from B-flat to D…

-     The student should use a tuner to correctly measure the pitches of the desired notes. At the same time, try to memorize the sounds of major seconds so that you won’t always have to rely on a tuner.

-     After you have learned the techniques, apply them in the exercise and the corresponding folk song. 

-     Always start in a slow tempo – only gradually speed up when you play everything correctly (right pitches, sound quality, left and right-hand techniques, etc.) until you meet the required tempo of the piece.

Every day for two to three weeks (two to three hours per day) depending on your schedule and capability.

MUA SAP - XOE HOA (CHERAW DANCE - BLOOMING FLOWER) is the music used for a number of dances of ethnic minorities in the North-West region of Vietnam, which can be found in festivals, ceremonies, and important occasions such as harvest festival, the Lunar New Year, or bonfire nights during full moons. When participating in a blooming flower or cheraw dance, young men and women are free to choose a dance partner and stay close to each other. This is why the dance is also an occasion for people to express their affection.
The music of Mua sap and Xoe hoa is upbeat, cheery, and festive.

Ga gay (THE CROW OF THE COCK) is a folk song of the Cong Khao ethnic group, which is an ethnic minority group living in the Northern Mountains of Vietnam. 

This is a bright and innocuous folk song. The song describes the cock crowing every morning and waking up the villagers to prepare for a new day on the field.   

The music is bright and happy, with a quick tempo.