I want to get the latest file that's in the repository, and overwrite what I have locally. How can I do this with the git client?

If you want to overwrite only one file:

git fetch
git checkout origin/main <filepath>

If you want to overwrite all changed files:

git fetch
git reset --hard origin/main

(This assumes that you're working on main locally and you want the changes on the origin's main - if you're on a branch, or your project uses the old master main branch name rather than main, substitute that in instead.)