Go to the Move Deleter in Canalaeve City. He will make your Pokemon forget any moves and is the only way to forget HM moves. If you want a move back (not including TMs/Hms) go to the Move Relearner in Pastoria City with a Heart Scale, which can be found underground.
The HM dive cannot be acquired in Pokemon diamond.
the one with the boat
whirlpool is not classified as a HM in that Pokemon series, only in heartgold/soulsilver is it a HM, in diamond it is only a simple TM (1use)
you have to find the man that deletes any move
move deleter in lilycove city
first of all there like ten Hm
i think there is a guy in solaceon town who will do that
"Talk to the move deleter."
The HM strength
Bibarel + SkuntankorBibarel + Drifblimthere is no hm slave
They disappear forever.
HM05: Defog