If you try to push the rebased master branch back to a remote repository, Git will prevent you from doing so because it conflicts with the remote master branch. But, you can force the push to go through by passing the --force flag, like so:

# Be very careful with this command!
git push --force

This overwrites the remote master branch to match the rebased one from your repository and makes things very confusing for the rest of your team. So, be very careful to use this command only when you know exactly what you're doing.

One of the only times you should be force-pushing is when you've performed a local cleanup after you've pushed a private feature branch to a remote repository (e.g., for backup purposes). This is like saying, "Oops, I didn't really want to push that original version of the feature branch. Take the current one instead." Again, it's important that nobody is working off of the commits from the original version of the feature branch.