surf from olivine to cianwood
You CAN NOT become a Gym Leader in Pokemon HeartGold and SoulSilver or ANY MAIN SERIES POKEMON GAME.
Not enough info: which gym leader?
In the goldenrod gym.
beat gym leader
Brock.
travel up the left side of the gym and hit the red button at the top
defeat gym leader.
in seafoam island
Jeff Gordon
He is the Gym Leader in Cinawood.
in blackthorn city
Simply beat the gym leader in every gym.