HOLD IT!
As your 10th breath (or as #11 if you want) take the BIGGEST FUCKING INHALE YOU POSSIBLY CAN AND HOLD IT IN.
I don’t mean hold your breath as long as you can while you’re just goofing around or seeing how far you can go in the pool. I mean hold your breath until your brain panics and forces you to let it out. If you can’t make it at least 30 seconds, you have no hope. The secret is inducing a survival reflex to breathe.