Does this car have a scissors jack or can you borrow one? Can you see the point of impact where it was hit? If yes to both, you will need a 2x4 or similar piece of scrap wood. You also need a saw.
Lay the jack down on its side with the bottom resting against some structure in the trunk opposite the point of impact. Then cut the wood to fit between the inside of the trunk at the point of impact to the top of the jack. With the trunk lid closed, jack the point of impact back into place, plus a little extra (1/8" to 1/4") to account for spring back. Go easy, you can always go a little further if the first time wasn’t enough but you can’t go less if you overdo it the first time.
If you have back seats that fold forward, this can get a little tricky. You may need to find some structure under the back deck lid.