To synchronize agent to your Quickbooks, click "Settings" on the sidebar, and then click "Accounts".
You can do a bulk synchronize by doing a search for accounts you want to sync and then pressing "Synchronize to Quickbooks" in the actions menu. You will receive an email when all the agents are done being synchronized.
You can also synchronize singular agents by clicking on their names and going to the actions button at the top right of their edit page and clicking "Synchronize to Quickbooks". This will immediately do the synchronization and will not send an email. 