repopulate dedleted field.

repopulate dedleted field.

Hi, I need some help figuring out how to repopulate a deleted field.  I have two forms, Assignments Form and units form.  The units form holds information about the unit "Unit_number, Unit_size" Th data entry, Assignment form holds information about Task assignment" Assignment_number, Unit_number , Unit_size. 

I accidentally deleted the "unit_size" filed.  from the assignment form and now I don't know the Bedrrom Size of the unit assigned/booked.   

What method could I use to repopulate this filed?  The unit_size filed on the Assignment form is fetched from the Units from and inserted automatically when the coresponding unit_number is selected. 

Thank you very much.