Measure the length of the bamboo , and decide the position of the finger holes.
I always calculate the position of the hole as shown below.
I think it depends on the shape and kind of bamboo, so you will do a trial and error here.
In this case, the fingering is roughly as shown below.
(in key=B♭)
Based on the results of the calculation, make finger holes on the bamboo with a drill.
After making all holes, attach the mouthpiece to the bamboo with glue.
When the glue is dry, let’s blow it .
It’s still out of tune at this stage, but it should sound pretty good.