substitue item in order management issue

Summary:

Getting error while doing the item substitution directly in Fulfillment lines,We have enabled flag 'Allow item substitution' as well. How the item substitue work directly in order managment. if we do directly its throughing error everytime. How we can use substitute functionality?

error:

The source line couldn't be updated because an item can't be changed when it's in an existing source line. (DOO-2685294)

If we have to unschedule the line, substitute and then change the warehouse, it'll take longer than if we just make all these changes