If they took your I-485 filing then they'll RFE you for it or send you a courtesy notice to bring it to you to an interview. (Note that getting an RFE is a good indication that they might waive the interview that's not absolute, I got RFE'd for medicals and then interviewed regardless, though in my case I had an EWI and prior removal proceedings).
Right now they will reject a filing without the medicals - not deny, reject, they will take your whole filing, put it in an envelope, and mail it back to you.
It's I-765. I-751 is a different form (removal of conditions for permanent residence)
Do you need a C31? If you have a C9 EAD then just use that one and renew it as needed.
If you don't have a C9 you can file the initial for that at the same time as C31 renewal. Reason for this is two-fold: C9 is valid for 5 years, C31 does get automatic extensions when you file a renewal, so a renewal would bridge any gap.
If you want the C31 just because (peace of mind, fallback in case you lose the C9, etc) then you can file a renewal and don't let me stop you.
These (all VAWA EADs) go to
For USPS:
USCIS
P.O. Box 87426
Lincoln, NE 68501-7526
For FedEx/UPS/etc:
USCIS
Attn: I-765 VAWA
850 S St.
Lincoln, NE 68508-1225