I just had the same issue with the tempering valve on the EFM. Began loosing hot water under high demand a few weeks ago, yesterday had a lukewarm shower. I was about to remove the guts but I got the hot water running at a good flow and rotated the adjustment stop to stop a bunch of times. Hot water is back now.
To answer your question: There should be a tag on the handle with arrows telling you which way to turn for warmer and for cooler.