When you try to open Tools > CICS > Resources Definition window, you are asked for user and password. The same happens if you try to open PCT or PPT in the CICS tab in Mainframe Express IDE. The project is local and the resource definitions are located in the config folder on the PC.

You will need to use "SYSAD" as user and "SYSAD" (upper case) as password.  These are the default set in Mainframe Express.  This will unlock the CICS Resource Definition file and you can again view/modify the CICS tables.  User "SYSAD" has system administrator privileges and owns all security and resource keys.