First develop a regular Select Query of the appropriate tables, that has a new calculated field 'Owner'. You don't explain the logic in determining the Owner so we'll presume you have a handle on that.
When you run this query - that Owner field should be populated correctly for all 16k rows. That is the first step.
Then you make an Update query. While some will suggest possibly modifying the Select query to an Update query I tend to think it is safer and easier to create a new query. You begin with this new query as the record source and set it up to update
your table.