You can have your Butterfree relearn Tackle at the move relearner, but Tackle isn’t that good of a move, especially not on Butterfree, and it’s probably more worthwhile to just level it up some more to learn new attacking moves. You can view its level-up moveset and TM list here.
the Move Deleter and Move Relearner are in the house north-east of the Pokémon Center in Dendemille Town. The Move Deleter is the old man on the left, and he'll delete any move for you. On the right, the woman will reteach your Pokémon any move in its level up for the price of a single heart scale. In addition to that, she will now help your Pokémon remember any Egg Moves they once had.
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