- F-Droid
- settings,
- repositories,
- See guardian project official releases; verify checked
- tap on “guardian project official releases” line
- See a list of more info
- scroll to “Official mirrors” list
- touch and scroll the mirror list
- uncheck all except one mirror
- go back to F-Droid display of Tor Browser
- Tap update
- If “not found” error, repeat with a different one mirror selected.
- Repeat until it works, or every mirror fails.
There should be about 7 mirrors to choose. If none work, you have a different problem than I did.