How is “add on” used?

In Argo (2012), one line is: “And then add to that.”

Which movie is “add on” from?

The clip at the top of this page is from Argo (2012).

Phrasal verb

to include or attach sth extra

Se oye en 295 películas

add sth on (to sth)
to include or attach sth extra
A service charge of 15% was added on to the bill.

Definiciones del Oxford Advanced Learner's Dictionary, 9.ª edición

And then add to that.

En 8 películas · n.º 1