If you are talking about how to defeat Gym Leader Jasmine, here are some things that will help you.
Hope this helps!
You can challenge the petalburg gym after you beat fire type gym leader in lavaridge town.
Beat The Lavaridge Gym Leader then May will give you the GoGo Goggles(:
you need to beat flannery at the gym in lavaridge town
The 4th gym is in Lavabridge town, the fire gym.
In the Lavaridge Town gym.
In the southwest portion.
It is in Lavaridge Town
Lavaridge Town.
Lavaridge Town.
Beat the Gym Leader at Lavaridge Town, then Brendan/May will give you Go-Googles.
In the lavaridge town gym.
The 4th gym is found on Lavaridge town and the gym leader is Flannery.