I had created a new repository in GitHub and forgot to add the .gitignore file to ignore all my Visual Studio and debugging files. However, I did not realize it until after I created the first commit.

These are the steps to apply the gitignore file later:

1. Create a .gitignore file in the root of your local repository. Run this command. This removes everything from the index:

   git rm -r --cached .
   

2. Re-add all files. Now the files and folders from gitignore are ignored.

   git add .
   

3. Then commit the changes again and push it to your GitHub repository

   git commit -m ".gitignore is now working"
   git push