Need help. Paint problem

Hi does anyone know how to fix this? Why does the paint in the lower face corrupted? And when I render it it stays that way. But the paint in the upper face is totally okay

What you show is called Z-fighting. There are two faces sharing the same location and your graphics card can’t figure out which one is supposed to be in front of the other. Probably you need to just delete one of the faces although that’s impossible to tell for sure from a screenshot.