Go to Canalave City/Town (I can't remember what it is at the moment) and go down to the first house you see. Talk to the man inside it, and he will delete any move (TM or HM)
OR, you can go to Pastoria City and go to the house with a fat guy standing outside. Go in, and talk to the fat guy inside it. If you have a Heart Scale in your bag, he will make your Pokemon remember a move it has already learnt or been taught(TM or HM) but you can't overwrite HM's this way.
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teach a flying Pokemon defog and use it
You have to walk the egg until it hatches then put it in the PC because otherwise eggs die in the PC.
Why do you want to get rid of pokemon in a pokemon game? That sounds useless... If you mean you caught too much pokemon you go to "PC" (in any pokecenter) and choose release pokemon.
you cant
Missingno is a glitch in the Pokemon series. It cannot be gotten rid of. Once it is in your game, it will be there forever.