Welcome to UtterAccess
You should have linked the 2 tables with a unique ID field. What you have to do now is create a unique ID field for the customers table as a primary key and add the ID field to another table as well. This is a one-to-many relationship. Then go to each cutomer and fill its related records in another table and field in the ID field with its ID. Do the same thing with the other cutomers. If you don't do it now, you'll be in trouble in the future when records growing up.
I know it's tedious but you have to do it and then you can do what you want later easily.