The user name of the computer is entered automatically and can't be changed. The Email Address is the address the Trial License is sent to. After clicking on the button "Extend Trial" the available information is sent to Moth Software.
Mail Archiver X support will send you a license file, which you should save somewhere. Select the menu item "Reset Trial Time". This will show a file open dialog. Select the license file and that's it. This can only be done once with a license file.