How do I manually reset the administrator password?

You will need to manually update data into database. Open users table and find your administrator user (by username). Update that row and set:

token: 0a92df346e3a833cae214d65af35e69b3cf4e5ab

salt: 6d093346fa02f

twister: 4982716305

That will set password to '123'. Login and update you password. Make sure that mailing is working (you can use Test mailing configuration tool in administration).