Please help. New recruit advice desperate parent!

Good morning and thank you for allowing m to join.
Please forgive me if I haven’t posted in the right place.
My son signed up to join fleet and passed everything. His careers officer then asked him to change to sub saying it will get him in quicker. So being young and eager he said ok. He should have been going to Raleigh next March but he’s now starting week two.
He’s had a couple of panic attacks and is regretting agreeing subs and he really wanted fleet. Has spoken to PO to see if he can change and they said no he can’t. But now they’re saying he may not be fit for subs. But I know he’s only panicking as he doesn’t want subs.
He has never had anxiety or anything before but now they’re telling him it’s genetic disorder!!!!!
I don’t know what he can do or what I can do?!!!
Please please I’m begging for advice!
Can I speak to them? Or is that a big no no?
Thank you in advance