I just wanted to shoot a video with a high frame rate on my Mavic Pro when I later realized that my Mavic had automatically slowed down the footage. later in post-production, i tried to speed up the video but had no clue how much the footage was slowed down by... if you know the answer please HELP!

I've never heard of any way to shoot in slow motion with the Mavic.  I only do it in post.  Are you sure you didn't do something like that?

No, don't Recall That. I simly set my Mavic to 720p 120fps

How are you playing back the footage ?
Whatever video software you are using is playing it back most likely at 25/30fps ... So to get it back to the speed you recorded at just increase it in divisions of 120fps.

120/30 = 4x

I have tried that it doesn't seem to be right. will try again right now and see what happens...

Same Deal, this time 1080 96fps

Are you playing it back just within the DJI app , or the full version off the SD memory card ?

When you shoot at 1080P 96fps or 720P 120fps, it will generate a slow-motion video. You can refer nottuppaware's answer on 4# to calculate the speed.