How cam I make this flat ?

Hi

I was wondering if you could help me. I have this pendant. I’m having a
lot of trouble trying to get it supported for printing. I can’t lay it
flat because the lines in the back are raised. How do I fill in the rear
of the piece so it matches the height of the back lines so it’s all
level so I can print it flat ?

My problem is my eyes. Have bad issues with them. They really can’t take
looking at a screen very long at all so if you have any button by button
advice on how I can do that so I don’t have to stare at the screen
that long I’d greatly appreciate it

You need to select the all back faces and press S -> Y or X -> 0. You can message me if you need more help.