Update data in a text box on a Numbers template from a table in another sheet

I am trying to create an invoicing model that will fill in a customer's name and address that is generated using the lookup function in a table on one sheet to fill in a text box on a template that has mixed text boxes for the address etc and tables for data. Typing = doesn't work as it seems not to be a cell but is a text box. Can anyone help with this? I have scoured the Numbers manuals online but can't find anything. I know how to do this from table to table but not to a text box that was on a template I downloaded.