It’s been a long time for me…but the only way to fix that is: Case off, be a very flat metal surface, plus a plannishing hammer. You would have to be super careful and use the flat surface, there are old fashioned panel beating tools that would also do it. It doesn’t tool to be a dent that will pull or press out.
You might be able to do something at home, if you have a flat metal surface and a flat metal object about 1 cm larger than the entire dent, place the flat object on it sandwiching it between the metal and the flat object…then rapping the flat object with a hammer.
Or go down your local car bodywork shop and ask one of the panel beaters to tap it out for you…which they will do in a few minutes. It won’t be perfect, but you should be satisfied with it.
P.S. If anything you use is not absolutely flat and the case not firmly down on it…you will get a poor result.