Hi Patrick,
I would suggest:
Create a (pop up) page with a data view of the object.
Within the data view set a List view of the selectable entity (You can add selection restrictions in the configuration of the list view).
Have the ‘On click’ action of the list view be a microflow.
Set up the microflow to with input parameters Object of the Dataview and Selected Object . You can configure the on click action to pass on these objects to the microflow.
Set up the microflow to change the association of the main object to the newly selected object and then close page.
I hope I understood your problem correctly and this helps. cheers