Update client runtime db from developer db

We have added new columns to a table in our developer db. Now we need to get these columns into the client's system without losing the client's existing data.

Their computer is running on Access runtime and we have split the db into FE & BE. We're quite comfortable copying the changed FE into the client's system, thereby overwriting and updating the forms, queries etc.

We have made changes to the BE schema, i.e. added new columns. How do we update the client's BE without losing their existing data?

Does MDE help? Package Installer? Some other way?

I'd be grateful for any help on this. I've not yet found anything on this topic, maybe I'm not yet posing the right question. Microsoft has thought of so many things in Access, surely it hasn't overlooked what must a common scenario for developers?