Hello,

The problem is the format of the current file being within the same product year, you can try with no guarantee to make a copy of the original file either using copy and paste or save as and placing a copy on the desktop.  Once this is done try changing the extension of the file from a .GB8 to a .GB7, after carrying forward please make sure to check all the forms to ensure the carryforward was successful.

You can save a copy of your 2018 under a different name (eg.  Mary Jones 2019 partial).  This will then have all of the 2018 data as filed.  It will not 'carry-forward' but you at least have the template and can insert your carry forward numbers as required and then complete the 2019 data entry and print to file the partial 2019 return.  

but how can I change the extension?

@bubblyfox Right click on the file on your computer and select "Properties". You can change the extension at the top of the pop-up that opens.