This is a do-it-
Your own video, how to clear the sink when it's blocked.
First plug the sink plug so there is no water flowing into the drain.
Now put a bucket under U-
Bend and remove the bend by rotating the coupler.
If there is water at the bend, it will fall into the bucket.
Remove blocked waste with twizzer or any other device.
Check whether the vertical pipe of the sink is blocked or the exit of the wall.
Clean all the respected places so it can flow water freely.
Repair all the parts again.