QE can only treat periodic systems, so one is usually working in supercell approximation. To get thin films you should more or less keep your input file and increase the cell in  one (Z) direction. You can always visualize your system with programs like XCrySDen.

thank you Mr. Ivor Lončarić

Adding to the statement of Mr. Ivor Lončarić, you should maintain sufficiently such way that electrostatic potential should be flat (sufficient vacuum between two periodic images) along perpendicular to thin film (here, it is Z direction). I hope this one can cross check with post processing of QE application.

How to generate input file for QE?