If you are trying to shift values from a dedicated to an ITFK, and you already know your configuration, you could do something crappy but functional like this:
Note: foos has the ITFK, bars_foos is the join, and bars is the other table
Code:
UPDATE foos
SET foos.bar_id = (SELECT bar_id FROM bars_foos WHERE bars_foos.foo_id = foos.id)
I hate using subqueries unnecessarily, but sometimes they solve the problem quickest.