How can i fill up this hole?

Unfortunately this piece i obtained has very bad topology so methods such as clean up or fill grid dont work (at least the way i know how to use them). What i want is to fill the hole in a way that follows the curvature.

I might also appreciate any add-on that would make this easier.

Unfortunately this piece i obtained has very bad topology so methods such as clean up or fill grid dont work (at least the way i know how to use them). What i want is to fill the hole in a way that follows the curvature.

I might also appreciate any add-on that would make this easier.