The file exists in the repository, but you don't want to submit it every time you modify it (such files are generally files related to the local development environment), you can do this:
1. Open the .git/config file
2. Increase
[alias]
ignore = update-index --assume-unchanged
unignore = update-index --no-assume-unchanged
ignored = !git ls-files -v | grep "^[[:lower:]]"
3. Run git ignore filename
This way, the changes to this file will not be committed when you commit again. If you need to submit this file again, run
git unignore filename