Mapping Key Resolution from UNSaccountB to UNSGroupB to get ObjectGUID


I've made a connector which only works with the Users class.
The UNSGroup assigned in One Identity has an ObjectGUID, which I have to map when inserting av new user from One Identity to the target system.
Please note that the groups on the target system is not standalone groups, the groups given to the user is based on a code (the code in ObjectGUID) when inserting the user.

I've tried with the key resolution from UNSAccountB - UNSGroupB, but im stuck for now.
How can i use Key resolution or Key Resolution by referance to retrieve the code in ObjectGUID on UNSGroupB from UNSAccountB? Is it possible at all?