If you click the Connect to CoA button in the secondary actions menu on in a Cargo Drawer,
you will open the Connect to CoA modal:
When you have connected the cargo to a CoA Line, you will see at the top of the Cargo Drawer a chip that says Contract of Affreightment as well as which CoA Line you've connected it to (40129002 in this example).
The CoA number chip (40129002) is a clickable chip that will open up the drawer of the CoA.
In this modal you choose which CoA Line you want to connect the Cargo to and click .