In lilycove city, by the dept store, there is a house labeled move deleter. Inside there is a man that deletes even HMs
Fly is an HM move - HM moves can't be forgotten by replacing it with a new one. Instead, you have to go to the move deleter to forget Fly, as is the case with all HM moves.
u get them all by defeating all 8 gym leaders
TM's are technical machines that teach your Pokemon moves but they can be used only once but you can get lots of them where the HM's there are 8 of them and can be used forever and these moves can be used outside of battle but can't be removed unless you go to the move deleter.
there is no such thing is a HM called remover
You can only migrate a Rayquaza that knows a HM move if you delete the HM move by going to a person who will delete moves for you including HM moves. In Pokémon Ruby, Sapphire and Emerald, this person is in Fallarbor Town and in Pokémon FireRed and LeafGreen this person is in Fuchsia City near the Pokémon Center there.
You use HM's just like you would with TM's, you click A on it and select use, then you select a pokemon who you wish it to learn the HM, then once it learns it you will be able to use that move outside of battle and inside of battle. TM's are one use only and should be used with caution. HM's have an infinite amount of uses, but cannot easily be forgotten, as they can only be forgotten by the Move Deleter
aggron learns strength,rock smash,surf -hm movesheadbutt,metal claw,roar,rock tomb,etc. are te other tm moves
Wobbuffet is unable to learn any HM/TM except the breeding moves taught to Wynaut, Counter, and Safeguardfrom the Move tutor for one heart scale in Fallarbor
You get the HM waterfall in the same cave you get Kyogre
Alakazam cannot learn any HM moves.
Moosdeep City.
the hm cut is in one of the houses in rustoboro city