Have you talked to all the important NPCs in Pal Park then? Maybe you need to do that first to activate that option.
@ Amore - I'm afraid not. It only works for moves naturally able to learn by level up (or level 0 moves for a Pokemon, e.g. ampharos can never learn fire punch without a move tutor without the move relearned, iirc for sake of example). Stuff forgotten that's not part of the level-up moveset alone cannot be remembered.