After Fuchsia City in Pokemon FireRed, players typically head south to Route 19, then surf east to reach the Seafoam Islands. From there, they can navigate through the islands to eventually reach Cinnabar Island, where the next gym is located. It is important to have surf and strength HMs to progress through this route effectively.
The answer depends on if you took on Fuschia after Saffron or before.
If before: Head to Saffron City, to get access to the gym you will need to defeat all the Rockets, your Rival and Giovanni at Silph Co (the massive building in the centre of town). Once that is complete you can challenge Sabrina in her gym.
If after: If I remember correctly you will need to Surf via Pallet Town to get to the next Gym in Cinnabar.
YOU FIND IT IN FUSCHIA CITY NEXT TO THE WARDEN'S HOUSE
In Area 3 of the safari zone in fuschia city.
go to fuschia city
you need to get the badge in fuschia city
You can catch it at the Safari Zone in Fuschia City but it is rare. Throw rocks at it and make sure it doesn't flee so you can catch it easier.
FUSCHIA CITY IS IN FIRE RED & LEAF GREEN NOT SAPPHIRE..VERONICA
YOU FIND IT IN FUSCHIA CITY NEXT TO THE WARDEN'S HOUSE
In Area 3 of the safari zone in fuschia city.
Sabrina
On the Route South from Lavender to Fuschia City a man in a house will give you it.
To the man in fuschia city that speaks like "mmphmmmphmmph" in one of the houses to the right of the pokemon center
go to fuschia city
it is the warden in fuschia city
They go to Fuschia City in the Kanto Region where the Pal Park is, where it used to be a Safari Zone.
Go to the move deleter's house in fuschia city.
If you mean the game warden, go to the southern edge of Fuschia City, he should be in his house.
you need to get the badge in fuschia city