If the file contains a single line and that single line is the word “exit” then it sounds broken.
You have two options.
- You just want to get a working system again.
- You want to persevere with trying to install this software.
For option 1,
sudo rm /etc/apt/sources.list.d/polychromatic.list
and that should be it.
For option 2,
Please link to the web site where you got your information about what this file is supposed to contain and what steps you are to take.
My next question will probably be: which distro did you choose in order to follow instructions?