In Pokémon FireRed and LeafGreen, you’ll get HM06 Rock Smash by talking to an elderly man standing in the back of Ember Spa. This spa is located on Kindle Road, just northeast of One Island.
Note that you’ll first need HM03 Surf before you can reach Kindle Road, which you can access after you reach the Sevii Islands.
There are actually a few things you need to do before obtaining Rock Smash. The prerequisites are:
- Obtain the Volcano Badge from Blaine on Cinnabar Island
- Have HM03 Surf and a Pokémon that can use it
- Be able to sail to One Island with the Tri Pass
If you can get to One Island and use HM03 Surf, then you can get the Rock Smash HM!
But if you can’t reach One Island yet, you need to make your way to Cinnabar Island and defeat Blaine in the Gym first.
Getting Rock Smash
After you defeat Blaine, Bill will show up and take you to One Island himself.
Once you’re on One Island, walk to the east coast of the island and use Surf.
Surf on the water just going northeast of One Island, and you will see a little trail. This is Kindle Road.
Once you land on Kindle Road, just start walking north. There are a few trainers here so you can battle them or avoid them.
The path is very linear, so just keep walking north until you reach a beachy / sandy area.
In this area there will be a cave entrance with a sign out front. This is the coveted Ember Spa!
Head inside Ember Spa and make your way to the very back wall.
There will be a man with a big white beard just standing there beside a couple spa baths.
All you need to do is talk to this man and he’ll give you the Rock Smash HM.
Note: To use Rock Smash outside of battle you need to have the Marsh Badge. But if you’ve made it this far then you’ve likely already defeated Sabrina in Saffron City anyways.