Users not backsynced.

The documentation has failed again to tell me what to do at the end of configuring the Azure Service.  

I have the backsync configured.  When I create a new user the account is created fine.  I can license a user and the soft-match occurs.  

Existing users do not appear to be linked with their Azure counterpart.  I'm guessing because backsync hasn't run but the documentation never says what the heck to do with the back sync config once its done.  

Am I supposed to manually kick this off?

Where in the docs does it tell you this?