Go through the gyn that's in the upper right area after u beat team plasma outside the gym then go through the maze in the gym and beat the gym leader
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
hearthome city
Fuschia city.
Hearthome City.
Petalburg 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
the badge is called the basic badge
Trade a Pokemon from an old version and make sure you have the fifth badge.