@baubergo-
If it's for an ad, you shouldn't change the original FPS to start with. If you want the professional ad look, it should be 24 FPS (in America) or 25 FPS (in Europe). Instagram's use of 30 FPS is just a weird standard that doesn't make much sense.
Of course, if you want to make an ad, you're going to need a professional for that. FPS is the smallest issue you'll encounter 😂