There is no such HM available.
Get the HM Rock Smash
Talk to a guy in one of the cities
From the secound house you see in Mauville City.
Beat the 3rd Gym, and Get HM 06 Rock Smash
in mauville, the house right of the poke mart, the guy inside will give you HM6(rock smash)
When you come into mauvill city from the soulth there will be a house to your left.The man inside will give you rock smash.
When you get to miavile in a house there is hm-Rock smash(beat Watson to use) then go to Vandturf, there will be a cave go in smash 1 boulder near the girl then the man comes accross and gives you hm-Strength
smash the rock inside the rusturf tunnel that is preventing the 2 people from each other
no Pokemon can learn rock smash by leveling up you have to get the hm.
You need to have Rock Smash, first. Then, go to the tunnel in Verdanturf Town. Destroy the rocks where the guy and the girl are standing, and he will give you the HM for Strength.
up your rump
(if they are breakable and you have the HM rock smash) go up to one and press A