You can't. Rockclimb wasn't in those games. HM Climb can be obtained on Pokemon Ruby, Emerald or Sapphire and later games.
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You cannot get it in Pokemon FireRed. It doesn't matter because it is not necessary in Pokemon FireRed.
you can find it in your bag where all your tms are.All the hms like rockclimb are under the tms.You can find hm rockclimb before you enter snowpoint city and after you get out of mount cornet it's in between there.
you get rock climb from professor oak after you beat all of the kanto gym leaders.
HM 8 doesn't exist in Pokemon Fire Red or Leaf Green.
Dive is not an HM in Pokemon firered or leafgreen however if you trade a Pokemon that knows dive from ruby or sapphire or emerald now you have a Pokemon that knows dive But you can't dive underwater in firered or leafgreen because it wasn't invented in the kanto region.