How do I forget a move learned by TM? Or are they permanent?

My pokemon learned Rock Smash from a TM.

I'm trying to learn Brick Break from another TM but I want to replace Rock Smash.

Apparently I can't forget Rock Smash.

So, are TM moves permanent or there is a way to forget them?

1 Answer

Rock Smash is a HM move.

You need to talk to the Move Deleter in Venesia (after the fifth gym) to forget that move.

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