Answer
To untrack a single file that has already been added/initialized to your repository, i.e., stop tracking the file but not delete it from your system use: git rm --cached filename
To untrack every file that is now in your .gitignore:
First commit any outstanding code changes, and then, run this command:
git rm -r --cached .
This removes any changed files from the index(staging area), then just run:
git add .
Commit it:
git commit -m ".gitignore is now working"
To undo git rm --cached filename, use git add filename.
Make sure to commit all your important changes before running
git add .Otherwise, you will lose any changes to other files.
Please be careful, when you push this to a repository and pull from somewhere else into a state where those files are still tracked, the files will be DELETED