Hi,
first of all I suggest to search the forum. There have been discussions about this.
I am riding for a lot of years and did a lot of scuffing tricks in the 90s so I am not the typical guy who learned pumping naturally like younger riders do it. But I tried to learn it. Now I can do it "more or less" but I am not fully satisfied. I asked a lot of riders how to do it and 90 % told me "just do it somehow, I can not explain". Nevertheless I will try.
Actually I think it can be done like this (thinking of a cross handed steamroller with the left foot on the peg, right hand on the handlebar, left hand grabbing the seat, so in a curve to the right):
Make the circle a little bigger, meaning turn the handlebar/wheel a little bit to the left (making the wheel more parallel to the frame). At the same time bend your left knee a little bit and let the seat/frame go down a bit. Then turn the bar/wheel back to the right and stretch the knee simultaneously. This has to happen quite fast. At the same time try to lift the seat a bit again.
It might happen that you make the circle very tight pretty quickly, so in addition it is helpful to turn your handlebar a little bit back to the left directly after the pump, but this happend more slowly. The action before has to happen quickly.
I hope this helps and would really like to know if this works for you. Please let us know.
Have fun and be prepared to fall