Hi AYBERK AKBALIK,
Change the value in position id . pass the respective parameter(Employee position) in the associated value field
In the change object, you first need the EmployeePosition object to be retrieved using '23' as the id and the set this object to that association.
The error clearly states that you are trying to pass a String to the association while what it needs is the Reference(meaning an Object of type EmployeePosition)
So before that change object you get 1 object of EmployeePosition from DB with id as 1, and then set it in the reference in place of '23'