If it makes you feel any better, I'm a HUGE PANSY when it comes to these things and even I fixed the crooked kneecap.
Just pull it off *very* slowly, holding down the rest of the surrounding rubber. You'll start to see the glue separate. Keep going slow. If it starts to tear the rubber (mine didn't) I'd say STOP! there and start re-gluing it back into place. The *correct* place. Because I'm betting that even if you only get it partly off, you can get it centered better.
Just make sure you use some quick drying glue. I used Super Glue No Drip Gel. There's also their Quick Drying Liquid, which is probably better for use on rubber, according to their own instructions. Just make sure the cap is firmly attached to the suit and apply some pressure there for a while. Maybe wrap a rubber band around it.
The MOST IMPORTANT thing, though, is to not dribble any glue ANYWHERE. So use just a TINY, TINY amount. And if that doesn't work, use only a TINY bit more. Because if you over do it, the glue will run out from under the kneed pad and then, I'll wager, you're screwed. Nothing that would remove the overflow of glue won't ALSO eat through the suit's rubber.