ArcGIS Monitor does not allow the creation of a new administrator account if the user accidentally changes the user type of all existing admin users to Viewer.

Workaround

• Browse to ArcGIS Monitor's configuration store (C:\Users\<ArcGIS Monitor account username>\AppData\Local\ESRI\ArcGISMonitor\config-store-<server or agent>).
• Open the data folder.
• Install DB Browser for SQLite on the ArcGIS Monitor machine.
• Right-click agm-data.sqlite and open with DB Browser for SQLite. 
• Right-click the users table and click Browse Table. 
• Look for the user account.
• Change the user type from viewer to admin. 

Steps to Reproduce