How to default value item in single select?

Summary:

I want to default a value item object in my single select. The premise is that on page load I want default a value in single select which stores currently selected value item object (not just a selected value).

Content (please ensure you mask any confidential information):

I have a header page with a single select in which user selects a Business Unit. But if they already created a record I want to load what is already stored in the Business Object.

When I store a direct selected value I have no problem. Trouble is that I'm selecting a "value item" which is an object with structure {key: key, metadata:{},data:{}}. And now I'm lost.