You can't unless you restart the game.
I have competed the entire game at least 3 times and there is no possible way to re-battle any of the gym leaders
No, you don't. You cannot face the Sinnoh Gym Leaders in HeartGold.
sorry, but there isn't a code to rebattle the gym leaders in diamond or pearl. there was once an attempt but, the leaders couldn't be rechallenged without you receiving the gym badge again. once you have two of the same gym badge the game freezes.
its a pity. you can,t! but if you like the music go on youtube.........
No
yes but only if you lose against one of the gym leaders
The Gym Leaders challenge you again in the Survival Area, The BattleGround which is locked until Buck lets you in then you can VS them again!!
Volkner
You cannot fight the Gym Leaders again in Pokémon Black after defeating them and being awarded their Gym Badges.
No there is not.
defeate all the gym leaders
beat all the gym leaders