1. In F-Droid, there is a Settings icon.
2. In Settings, choose the Repositories option.
3. Click the plus sign (+) to add a new repository
4. Add the repository:
https://microg.org/fdroid/repo
5. Make sure it is checked
6. Go back to main F-Droid screen
7. Search for microG Services Core and install it.
8. There are 3 other apps with microG in the name which you can optionally install if you want. I did not.
9. Optional. Go back to Settings | Repositories and turn off the microG services to keep F-Droid speedy.