Hi,
based on your requirement, you can follow any of the steps below
1. In PAI use can use the field statement as mentioned by Nikolay
FIELD Release MODULE assign ON REQUEST or
FIELD Release MODULE assign ON INPUT.
2. In PBO or PAI you can use the below code
on change of Release.
reference = release
endon
3.In PBO or PAI You can assign to reference when it is empty
if reference is initial and release is not initial.
reference = release
endif.
Regards
Anand