How do I derive a discount based on the customer's ship to site number?

Summary:

My client needs discounts based on the ship-to-site number.

Example:
If the ship-to-site number = 1234, then there should be a 10% discount.
If the ship-to-site number = 5678, then there should be a 20% discount.

Content (please ensure you mask any confidential information):

I found a note that mentions that it can be added within Manage Matrix Classes, but it seems I'm missing the domain.

Version (include the version you are using, if applicable):

25B (11.13.25.04.0)

Code Snippet (add any code snippets that support your topic, if applicable):