Learn to keep stroking
Keep it at a good stroking speed and listen. The first thing you have to do is to approch the edge slowly, if you wank towards it fast, you'll risk going over it with one quick stroke. So when you feel your cum boiling up, and the edge is near, slow down.
But not too much, slowly slow down, in a way you are still increasing your arousal but by smaller steps. And you probably want to keep away from your glans and the sweetspot behind it. Try to stroke your shaft only when you are near.
And when you hit the edge, go slower, probably walk one step away from the edge, then go a bit faster again to walk towards it, then slower. Gently strokes only, but keep moving your hand. You have to slowly find a speed that keeps you on the edge, without walking back.
Try for a Minute to find that speed, but don't you dare push yourself over the edge!!
Then ...