Dented rear passenger side quarter panel

[Dlip]

Hi, new member. Yesterday, after replacing my interior mats and having the car cleaned (light detailing) it looked like new. Then last night I managed to put a large dent in the rear passenger side quarter panel from above the fender to the antenna mast, about 16" in diameter. Since it is an integral part of the car (welded, not bolted) I wondered if anyone had any insight on accessing the area from the inside to facilitate a repair. Thanks