SHELL

git remove file from repo that has been added to gitignore

Commit any files that you need to change/delete to the repo. Then:

git rm -r --cached .  # this will clean all files from cache. To clean a single file, exchange '.' with filename
git add .  # add all of the now uncached files that are not gitignored to the staging area
git commit -m "fix .gitignore"  # commit the changes