VenumPredator Mouthguard, One Size

Are they one size fit all or this is just for youth?

I have a retainer behind my lower row of teeth. Would this damage it? (And vice versa)

Does it have the mold part in it already?

Hi, I bought a Venum Predator mouthguard and I want to mold it. Bu t i lost the instruction of how to mold it. Can anyone help me with it? Thanks!