Easy? Tutorial? Remove? Mmh...
a) There's no secret hidden info under the flare. Blown out areas will not magically bring back the face and as per your words the damage is severe.
b) If at all, a local color correction with masks may serve to even out the differences, but not entirely remove the artifact.
c) Additional cloning, rotoscoping and masking may be necessary to "repair the defect. This can quickly look iffy when not done right and requires experience.
With all of that you see that there aren't going to be any quick fixes and based on what I said, I don't think there can be a tutorial for this specific case, but of course you can find ones on the individual techniques. Either way, without seeing your footage nobody can advise specifically.
As Mylenium said, without seeing your shot it's impossible to point you to anything but a general solution. That solution will most likely involve tracking skills, a fairly thorough knowledge of how the Clone tool in AE works, an understanding of basic compositing using layers, a good understanding of color correction techniques, probably some rotoscope or track matte work, and generally a very good understanding of where all of the switches and levers hidden under the hood are located and how they work. There is no one click solution for most shot cleanup work.
Here is a tutorial from my friends at Video Copilot that shows you how to put an evil alien skin on a face. Depending on your shot you may be able to use similar techniques to remove the lens flair. If your shot is anything like this one from Adobe Stock:
then it's going to take a lot more work to clean it up.
Post your shot and we can give you better advice.