The backorder message in the item record is updated. Updated the backorder message in the item record using Mass update. Allow back orders with no out-of-stock message is Set as the value in the field out of stock behavior in the item record. Created a workflow to set the value Allow back orders with no out-of-stock message as default while creating a new item.
Solution
A mass update is performed to Set the out of stock behavior in the item record as . Allow back orders with no out-of-stock message.

A workflow is created to make the backorder message set for the new item that is adding.

- Record type:Item
- Event:On create.
Action:
event:Set field value-Out Of Stock Behavior=Allow back orders with no out-of-stock message