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 .
$ git commit -m ".gitignore is now working"
*Note :- Be sure to merge your branches back to master or move your pointer otherwise you might lose your branch