There is no way to recover a lost password for the admin account in SynaMan. The Forgot your password link on SynaMan's login screen only works for regular users. It does not work for the admin account.
However, following the steps below you can reset the password for admin to a different value.
Steps to reset
You must have access to the machine where SynaMan is installed
Stop SynaMan.
Using Windows Explorer on Windows, Finder on Mac and Terminal on Linux, go to the installation/config folder. The default location for this folder is:
Windows: C:\SynaMan\config
Linux: /opt/SynaMan/config
Mac OS X: /Applications/SynaMan.app/Content/Resources/Java/config
Locate a file called AppConfig.xml and make a backup copy of this file. You are about to modify this file. This backup copy will come in handy if you need to rollback.
Connect to the web interface from a browser on the same machine. The URL should be similar to http://localhost:5800. When connected, SynaMan will run the setup wizard again and will ask you for a new password for the admin account.