Migrate Canton sequencer-mediator from 0.3.21 to 0.4.0

We are running a sequencer-mediator to form a custom domain apart from the global domain. Our participant node is connected to both the global domain and our custom domain. We want to migrate our custom domain as well from 0.3.21 to 0.4.x. What is the best route for that.

Thank you
Brij Chuahan