In reading the manual on my Suburban water heater, it indicated that was not a temperature control. Maybe there is something that can be overridden like EnudroRdr shows.
But, what I do- I just opened one of my winterization valves a little to allow some cold water into the line after the water heater. It knocks back the instant scalding hot to scald you a little slower. It's a little temperamental with inconsistent hotness of the water, but not at all unbearable. I like that I can worry-less about the little hands in my family. AND that I can do dishes when the wife runs the water for doing them (she thinks only hot gets them cleaner, I guess; I happen to like my finger prints).