How to display multiple IIf results in one column

I have a simple query for one table that I need to display different
results on multiple rows, but within the same column for several
fields. The below example I am trying is not working:

Result: IIf([field1]=yes, “abc”, IIf([field2]=yes, “xyz”))

I would like the query to display the following on two separate rows:
Result:
abc
xyz

What is the best method to achieve this without having to use a union
join query?

Thank you!