Were is the 7 gym in Pokemon Ruby destiny 4?

There seems to be a misunderstanding. There's no official Pokemon game called "Pokemon Ruby Destiny 4." It's possible you're referring to a fan-made hack or ROM hack.

If you can provide more information about the specific game you're playing, I can help you find the 7th gym location. Please tell me:

* The full name of the game: Is it a ROM hack or a different version of Pokemon Ruby?

* The source of the game: Where did you get it? Is it a website, a forum, or something else?

Once I have this information, I can try to help you find the 7th gym.