How can I fill in an object without issues? Thank you for your help!

[Brooke1]

Filling a hole in a previously made model

Hello, it’s my… idk 5th time using nomad and my first time using this forum in hopes to get the answers I need as I don’t know to explain my problem to google. Basically I found this shape of a head online, put it in nomad app, cool. But here’s the problem, the inside of it is empty. I lack experience for this app and all the terms are so new and confusing, but that’s why I’m here to learn. I have provided a sketch of my problem so it makes more sense. Thanks in advance, please use simple terms…

Check this page. Either re-voxel or trim a tiny bit with fill holes selected.
Hope it helps.