It doesn't look super deep in the pic, but maybe it goes in a ways? How deep is it? The first thing to do is get any water out. You should towel dry the area as best you can. Then, suck on it to see if there's still water in there. If you taste water or hear bubbling you need to dry it out more before doing any repair. Either way it should definitely be dry before permanently repairing it.
A quick fix is to use a solar-curing resin or epoxy resin like Solarez or Sun-cure or similar. On the other hand, if you're on vacation and don't have it on hand and just want a quick fix to get you back in the water until you can fix it for real, then you can use something like marine tape or a strong duct tape. I always carry a product call Dr. Phix's ding tape:
https://www.phixdoctor.com/product/phix-doctor-ding-tape/ I'm not sure that'll help you out where you are but you might be able to locate something similar at a marina or boat repair business. It'll prevent further water intrusion until you can do a proper repair.
The other thing to be wary of is whether or not the fin box is damaged. Again, it looks pretty small but you can check by putting a fin in and
gently wiggling it in all directions. If the fin plug creaks or flexes the surrounding area in any way then you should get it repaired properly.