I need to add this file on git (Android Studio Project)
This is my .gitignore file (root of the project)
git add -f app/build/outputs/mapping/my_flavor/relese/mapping.txt
You only need to use the -f flag the first time - .gitignore does not work for files that are already tracked.
However, I would recommend treating the mapping.txt file as a build artifact and NOT add it to version control, instead, store it along with your .apk file to wherever you are storing build artifacts.