Beat Byron then get strength and then you can use it.
HM04
the most probable mistake is that you did not beat the gym.
Well, first your going to have to obtain the Strength HM. Assuming you have that, teach it to a pokemon. Press A on the boulder you want to move and walk in whatever direction you want it to move.
Well any pokemon that can use the strength tm to move that boulder out of the way unless it's a big boulder you cant move that
This boulder is probarly a boulder you need the HM strenght for, which eenables a pokemon to move bulders.
one of you Pokemon in your party need to learn strength.
You can move that boulder by using the hidden move strength.
in the cave with big boulder
Boulder push is also know as strength. machop, machoke, machamp, geodude, graveler, and most any Pokemon
By using the move strength.
To move a big boulder you need obtain the move Strength. To use the move outside of battle you need the Rainbow badge.
In the game Pokemon Pearl, the HM move Rock Smash is required in order to break the boulders in Mt Coronet. To fully explore the mountain, a players needs Pokemon that know Rock Smash, Strength, Rock Climb, Defog, Surf, and Waterfall.