Thanks to the lead from @Ontapforrum , I joined the Discord and spoke with the Harvest folks.
For anyone else this happens to, just log into the appliance root shell, and use 'passwd' to change the local shell account password for 'admin', then, once you are able to use that to log into Harvest, then within the Harvest web interface, use the settings option to update the 'admin' account password again, so that the updated password is propagated out to Grafana.
If you only change the 'admin' password on the root shell of the appliance, you won't be able to get into Grafana with that admin account.
They mentioned updating the FAQ and Troubleshooting sections of the Harvest docs with this information.