Your Buyer can define contacts within their company (or update existing ones if someone leaves) for roles such as Billing, Shipping or additional Buyer accounts within their organization.
The Buyer selects "Contacts" from the drop down menu in the top right corner as shown below:
Then, they will click "+ Contact" or "+ Address"
Next, they fill in the pertinent information for the contact information and click "Create Contact":
The first address the Buyer enters will default to the Billing and Shipping address. This can be edited by the Buyer should they have other addresses to add:
If they edit, they simply deselect Billing or Shipping from that address and click Update:
If they deselect and/or add additional addresses, they will be able to click on "Make shipping default" or "Make billing default" for any one of them from their main Contacts/Address screen without having to go into Edit mode.
These are automatically added to the Contacts>Customer database for your Buyer's company. And, will be associated with every order submitted by this Buyer unless changed. Please note the "Accepted" indicates the one you approved as a Buyer. The other two contacts can be "Invited" to be "Buyers" if you want. Or, perhaps you just send them documentation for invoices and shipping & receiving documents without giving them "Buyer" access.
For additional information on Customers & Contacts, see our Customers Setup Profiles Knowledge Article.