Update itemsets in form


I have uploaded a form with external choices in itemsets. If I update the itemsets and upload the form again it gives error Form Already Exists for this Namespace/Id attribute org.opendatakit.aggregate.exception.ODKFormAlreadyExistsException: . But one of my another form does work well in this way if I update the itemsets and uploaded the form without deleting data.
Any hints how does it work. If possible guide me how to replace the itemsets in database instead of adding the form again and again.

You cannot have forms with the same ID. If you want to update an existin form, Update form version in Aggregate has a good overview on how to do that.

Thanks I had no idea of versions before. It worked.