Hi Sai,
in general, the owner of the association is referring to another object, ie. in your case you have to add the reference to the department. You accomplish this by performing a change action on the user, select the respective association and add the department. If you do not have the department available in your microflow, you have to retrieve if first from database or via association. Best have a look at some learning paths at academy.mendix.com, which give you more insights on how to develop apps with mendix
I solved my problem. my bad.. The research was frustrating, because the answer is too simple.
Just choose the association in the “change object” activity and then just put the object in,which you want to associate.
No equations, or special syntax..