How do you update a subform picklist, with values from rows in another subform?

How do you update a subform picklist, with values from rows in another subform?

I have created one form to gather information when on-boarding customers - one subform gathers information pertaining to user-groups, another gathers information about individual users. Each user can belong to several user-groups, which are created by adding rows in the user-group subform. How do I dynamically populate the picklist on the user subform with the information gather from each row in the user-group subform?

I've tried a variety of solutions that haven't worked - the most logical one to me is that on input of user-group_name, you use the script ----  User_Info.User_Groups:ui.add(row.User_Group_Name); ----- but this will only add the User_Group_Name from the first row. It does not add values from subsequent rows.

Any help is appreciated!