The photographic background paper is uneven and the film is like an indentation. Is there any way to smooth the background?

Simple, what if the clothes are uneven? Shall I iron it with an electric iron? In fact, paper can also be ironed with an electric iron.

If there is no electric iron, there is a simple thing to replace it, that is, to find a large enamel cup with a handle, which was common in the past, or to replace it with a flat bottom and half a cup of hot water.