How to color correct a corner in a video

Hi! I'm a newbie to Premiere Pro. I taught myself basic corrections through YT videos, but I have not been able to figure this out!

I have a video that has a dark corner. There is a person that is walking back and forth in the video and if I mask the dark corner, then it distorts the color of the person walking. I tried adding a vignette to highlight it, but then it distorts color in the three other corners. 

I was able to successfully adjust the color in the video so that the video looks great- except for that one corner! I know there must be a solution, so I hope someone in the community can help!

Thanks!