[Happybandaid]

How exactly does it work?

There's a move my Odonine learns at a level before it evolves, so it normally can't learn that move - I'd like to use the Move re-learner item to get it, but the item description sounds like it would reset all my moves..

This item will reset your move learning history. This item used monster will be able to reselect all previously learnt moves. "

I've taught this Odonine a couple expensive MT's, and I don't want to lose them! If I use the Move Relearner, can I get that lower level move I can't normally learn while keeping the MT moves I've used on my Odonine?

[shadowananime]

i dont konw but keep lvling up odnine he will learn even if he can evole

[I'm Hungry]

Yes you can keep the moves you already have if you use move relearner .

[Happybandaid]

Okay, thank you.

[Lolzinator]

The use of move relearner simply clean out the history. 
if your monster learns a move in lvl 5, but you have trained far past that and want it back, simply use a Move relearner and everytime you win a battle with this monster, you will start learning every move all over again.

The current moveset will not be affected in any way, other than if you switch it out manually

[CeFurkan]

it resets learning from 1 level again simple stuff