My .obj shows its "back" instead of a "face view" and Mixamo won't rig it.

Good afternoon,
thanks to one of your contributors I got a whole set of Harry Potter models but when I open the .objs, they show me their back and when I try to rig them in Mixamo, it fails (while when the .obj orientation is “normal” it works).
Could anyone tell me how to fix this?
Thank you in advance.