Delta shower system help - water not hot

Plumber finished up when I was not there. Not sure what all the SO and he did re: testing. Well, the water isn't hot enough for a proper shower. I learned there's probably a scald protection dealie in there I can adjust? The SO wants me to wait, but no idea when this guy is coming back. Here's my problem-I don't want to break this fixture, but I cannot get the end cap with the temp control off. Is there a trick? Do I just pry it off? There is no set screw. It looks a lot like this: