IIS port problem

Hi everybody!

My company would like to use MantisBT and i got the task to setup mantis but i have some problem with it.

I would like to run MantisBT on port 443 (https) but one application already use this port. (This application isn't based on IIS). The server which should run MantisBT has two network cards and using Windows Server 2019. The first (x.x.x.1) is used by the necessary monitoring application, the other one (x.x.x.2) should used by MantisBT.

The problem is if i bind x.x.x.2 IP to port 443 than i got an error message:
The process cannot access the file because: it is being used by another process.(Exception from HRESULT: 0x80070020)

Any idea what should i do?
Can you give me step by step advice?

Thank you. Have a nice day!
PN