What TC is trying to say… when reducing power, reduce your MP first, then reduce prop rpm. If you do it in reverse, you could blow your engine up as putting it in course pitch (reducing RPM) actually puts a higher load on the pistons and could break them.
When wanting to increase power do it in reverse, increase prop rpm first, then increase MP.
If you’re not sure what settings to use for each - “match” them up in value (but you really should get a POH and see what the recommended values are for various phases of flight).