Move Tutor sometimes called a move relearner by fans, is a character who allows Pokémon to relearn any move that they were able to learn from a previous level-up.
To get started make your way to Cinnabar Island and talk to Bill. Note: You must’ve beaten the Cinnabar Gym for him to appear.
After speaking to him follow the prompts and he will take you to one island, just walk up one step then walk back down and talk to him again, follow the prompts and select Island Two.
Once you are at Island Two head outside and to the left, after walking up the stairs you should see a house with a purple roof on your right, this is where you can find the Move Tutor.