Unscrew the needle from the air pump.
Insert the needle into the inflation hole on the volleyball. Air will start to come out. Remove the needle when the ball has the air pressure you want.
If you want to deflate the volleyball completely, keep the needle in place and gently press on the ball when the air becomes low and does not flow out on its own. Kneel on the ball or fold the flattened ball to press more air out.
When all the air is removed, pull out the needle while pressing on the volleyball. This prevents air from flowing back into the ball.