1. Go to Service locations tab under the Billing customer and you would be able to see a QuickBooks sync icon if the service location is already synced into QuickBooks. (highlighted in red)



2. If the service location is not synced into QuickBooks you can just click anywhere on the service location and the service location details page would open. On this page, there is a button where you can sync the service location into QuickBooks online. 



3. Once the service location is synced, the QuickBooks logo is updated on the service location details page and in the service locations list as well. (Highlighted in red

If the details of service locations are updated and to sync the updated details the procedure is the same, you just need to click sync to the QBO button.