How to import TurboTax return info from previous year into a current year return that is already mostly completed, on Desktop version?

I am about finished with a current year return, when I needed to make changes to my previous year return that has not been filed yet.  Now I need to import those previous changes into the current return.  

 

Can 'import previous' only occur when you first start a new return?  Why is there not simply an 'update/transfer previous year' info button?  I cannot be the first user to ever process more than one year at a time, with this type of issue.  It would be absurd to start over.  Otherwise, going forward each year, the past return info will always be incorrect.