I think I would put some stud locations below that wrinkle. That part has to come out as well. Pulling it out will close up the seam somewhat on the upper part, but that wrinkle will be the toughest part to get straight, possibly needing some access to the backside.
Before you proceed, I would wait for MPandC to weigh in. He would have better suggestions than I do. He may recommend cutting the wrinkle out completely in order to get it gone satisfactorily.
Good luck on whatever you attempt. The one saving grace is that you probably would have to work hard to make it worse than it is.
