Expenses with same expense types have different classes

Summary:

We have two expense reports with the same expense type but two different expense classes. How are expense classes assigned to expense types? I can't find a configuration for this anywhere in expense setup.

Content (required):

We have two expense reports with the same expense type but two different expense classes. How are expense classes assigned to expense types? I can't find a configuration for this anywhere in expense setup.

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

22C

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