If you know the model faucet, look it up on Moen.com. I usually go to
the section at the top called "Buy Parts Online", which will guide you
through a series of questions to identify your faucet. Then I go to
"Support" and input the model number I just found, and get the
detailed Instructions sheet/owners manual. By following these
directions you can avoid scratching the sink and damaging things by
doing things the wrong way. It also says about your problem: "To
Eliminate Cross-Piping on Back-To-Back Installations, or To Correct
Reversed Rough-In Where Hot and Cold Positions Are Reversed - Remove
handle parts and stop tube (see "Disassembly"). Turn cartridge stem
around so that the notched flat is turned one half turn or 180°.
Reinstall handle parts. Tighten handle screw securely; replace handle
cover."