Do you want to put a fresh coat on the whole underwater portion of the hull or just a few small spots?
If just a few small spots - you could probably get a away with sanding them lightly and using an ablative antifouling paint like interlux micron CF, Pettit vivid, or Sea Hawk mission bay. Trilux 33 would also work. It's the tried and true choice for many
if you want to do a full coat and have no way of knowing what type of bottom paint was used, Sea Hawk paints makes a product for this exact situation. It's called sea hawk 1277 bottom paint primer. It's super sticky coating that ensures good adhesion of your new coat of paint and compatible with almost everything. Also fairly cheap.
Main thing - just don't use antifouling paint with cuprous oxide. This stuff is the norm for plastic and steel boats but not good for aluminum.