Import CSV file and assign work items to the particular iteration
One answer
Have you tried to export some work items with planned for, then changed the planned for in RTC and then imported the old export?
If yes, what do you see?
If not, why not?
Comments
The work item command line supports this if the built in import does not. See https://rsjazz.wordpress.com/2017/03/29/the-work-item-command-line-is-now-open-source/