Thanks for posting.
Unfortunately, a setting does not exist in the Admin Console that allows you to reset the password.
One option is un/re-installing the software to reconfigure your FileMaker Server.
Alternatively, I would suggest the following:
1. Close out your databases in the Admin Console
2. Remove the FileMaker Server > Admin > Conf > .xml files.
3. Now, when you launch the Admin Console, you will get the Deployment screen and you can start your re-configuration of FileMaker Server.
This at least avoids the steps of having to un/re-install the software.
Hope this helps.
Remove the FileMaker Server > Admin > Conf > .xml files. Where can I find these files?