Can a Contact column populate based on selection in another cell?

I have two columns; Workstream and Workstream Leader. Their column types are Dropdown (Single Select), and Contact List respectively and each contains five available selections and are set to Restrict to list values only. I want the Workstream Leader column to populate with the contact that I know to be responsible for that Workstream.

How can this be accomplished? I was attempting this via use of an IF function, but that has not yielded positive results...