I recently had a half gallon stay thin, and decided to start over with it.
I heated it very gently, planning to add a little more yogurt and put it somewhere warm again, but noticed very quickly that it separated into curds & whey!
By the time it was up to about 100 degrees, I realized I could scoop out whey with a ladle. So I just poured the whole thing into a draincloth in a colander, and it became almost instant yogurt cheese.
With yogurt cheese I like to salt it and mix in some granulated garlic and whatever herbs are lying around.
This time I lightly salted it and left it plain so I could play with it. I've been crumbling it into omelets, and might soon use it in place of goat cheese on some pizza.