It's been more than a few years since I had a Pro-Plus, so I don't remember as clear as I would have liked. I thought that there was a groove on the computer itself, but I'm not positive. There are some pictures in this thread that might help. If the case looks similar, I would expect the process to be the same.
Following up on the great advice from @DIVEWATCHDOCTOR, here's where I am today. We did our pool session (12 fsw for about ten minutes) and the battery compartment, as expected, didn't leak. Today I took out the screws and removed the cover, and this is what I found. IMG_7548 by Jim Forte, on...
scubaboard.com
Changing a battery in a dive computer should not be something that a dive shop needs to do. Especially today. I could somewhat understand when they were first introduced and often oil filled with soldered battery contacts. But today, there shouldn't be a need to have a technician need to change a single use battery. If you want to continue taking the computer in for a battery change, that's fine. It shouldn't, however, be necessary.