Just bought a new house. The hot water was more like warm. Turned up the temp on the hot water tank now master bath is perfect but guest bath now has only hot hot water and not cold. Thinking I could turn the temp back down but then I would have a cold master bath and a good guest bath. Any ideas?

I think you must have a scald guard faucet, f so the temp can be controlled by taking the handle off and moving the temp setting, if you still have the faucet brochure it should tell you something.

The guest bath now has only hot hot water and not cold.
This doesn't sound like a adjustment to me. Sounds more like the cold water inlet ports on the cartridge are clogged. turn the water off to the mixing valve and pull the cartridge. Check and clean the inlet ports. now turn the cold water back on to
Flush out the supply. You should have cold water coming out of the open valve. If so reassemble and test. Good luck and thank you for rating my answer. Tom