You cant!
No. But, you can fight them (as gym leaders) In Pokemon Silver/Gold.
You fight him after you get 4 gym badges
You can fight Archie before he awakens kyoger
Fight, Fire and Ground.
you have to fight Pokemon you see hope this helped
Battle Tower, if that's what you mean.
You fight him after you get 4 gym badges
on the top floor in a white building
Sorry, you can't in Pokemon Heartgold. But you can in Emerald, Ruby, Saphire and crystal.
The trainer with Chimecho in Pokemon Emerald is located on Victory Road. When you go to Victory Road there will be two psychics that you will fight. After you fight them one of them will give you Chimecho.
then you have to fight wallace and then go to pokemon league
after you beat 4 to 5 gym leaders you can face him