Add already existing records to subform

Add already existing records to subform

Hi!

I have an app with a Parent Form "Clients" and a child Form "buildings".

Buildings it's a subform in clients, but also an independent form. There where records added to Buildings outside the Clients subform, so they do not apear there. How do i do to make does records in the subform? I allready tried creating a bidirectional relationship, but did't work...