The first thing to do, is to find the puncture - sometimes there'll be a hole visible, sometimes there won't.

Once you're happy there's sufficient tape (read: lots of tape) in place, inflate the ball. This is so that the bladder pushes the rag and glue against the shell You may find that it's not under the flap you've cut out - the initial test found out where the air was escaping from the shell, so whilst the puncture is likely in that vicinity, it may be off to one side. If necessary, carefully cut more access For best results on the next bit, as long as it won't affect your access to the puncture fully deflate the ball. Carefully press a craft knife against the foam to cut around the area - be sure not to press too hard as you don't want to slice into the bladder underneath. You'll need to cut into the ball to access the bladder. This is best achieved with the ball partially flat.

Why use a football puncture repair kit?

Inflate the ball and verify that no air escapes. You might find (especially if the ball has been into brambles) that there are multiple holes, repair those too