you just have to go to petaburg city and enter in the gym
In Pokemon Red, the fifth badge is possessed by the Poison-Type Koga. The badge is named Soul Badge. It lets you use Surf outside of Battle.
Hearthome
Fuschia city.
hearthome city
Petalburg City.
Hearthome City.
Beat the gym leader
The fifth gym leader in Pokemon platinum is crasher wake but you get the fourth badge.
You need to defeat Koga in Fuchsia City to get the 5th badge, the Soul Badge.
The fifth badge is in Sootopolis City, you need Surf, Dive, and Whirlpool to get it
Trade a Pokemon from an old version and make sure you have the fifth badge.
you should use either ground or psychic Pokemon