How to make set_query return certain field?

I have a doctype with fields Field1 and Field2 which have data structure as below:

      Field1 | Field2
     -----------------
         A       1
         A       2
         B       1
         B       3
     -----------------

I want to get the Field2 from other doctype with a Link field (with filter for Field1)

As you can see, the data is unique when Field2 is together with Field1.
I can use Auto Name such as format:{Field2}-{Field1}
But using this Auto Name will result in the dropdown displays Field2-Field1.
What I want is the dropdown to only display Field2.

The set_query script I use:

    frm.set_query( "linkfield", () => {
        return {
            fields: [ "field2" ],
            filters: {
                "field1": "A"
            }
        }
    } );

How do I achieve this?
What should I fill in the Auto Name, Title?
Or if I really have to use such Auto Name, what args should I use in the set_query script?

Thank you