Hello , As part of Open API , which API we use to update customer assets (on Customer master(Part or separate from CRM) once the order is submitted.
First, I recommend that you take a look at the Open Digital Architecture (ODA) end-to-end use cases, in the published document IG1228. This shows how the APIs are used in typical processes, including commerce flows. https://www.tmforum.org/resources/standard/ig1228-how-to-use-oda-using-open-apis-to-realize-use-cases-v13-0-0/
Specifically for your situation, customer assets are presumably what TMF refers to as Product , and they would be updated in the Product Inventory using API TMF637. It's probably wise to restrict access to the API's create/update/delete operations to software such as product order management - you would probably not want arbitrary updates being made in the product inventory.
Hope it helps