How to import new models ?

[r2d2m]

Hi, sorry to bother you, but I tried to import other meshes into unity, and I have a weird lighting : https://imgur.com/a/J48hIHU

I imported a skull in the default angle (1st image), then rotated it (2nd image)

It seems to be lighted from below. I have this problem with every model.

Do you have any idea ? Do I have to do something in Houdini ?

Thank you for your time