Auto Populate from Connected table

I have a number of Forms each of which has a connection to the Location table.

A user can submit multiple Form entries from the same Location, so to save having to keep selecting the Location from a dropdown on every Form I would like to set the default for the Location Field in the Forms to the first record showing in the dropdown. Then the user can leave it as the default or using the dropdown select one of the other Locations.

I have been trying for months to find a way around this but have been unsuccessful, does anyone have any suggestions?

Thanks,
Keith