Type your drop-down text here.
Step 2 - Drag the desired person/entity to the desired case in case navigation panel.
Hold down the left mouse button on the quick list entry that needs to
be added to the associated persons for a case and drag it to that case
in the case navigation panel.

Once the symbol that looks like a small white sheet of paper appears
let go of the left mouse button.

The item that was dragged to the case should now appear in the associated persons for that case.