After you complete your initial connection from QuickBooks Desktop to Timesheet Mobile, you will want to periodically launch the QuickBooks Web Connector and sync. new Employees and Customers to TSM.
The QB Webconnector is included in your QuickBooks installation and can be found in QuickBooks->File->Update Web Services (See below).
If you get an error launching the web connector or cannot locate it, you can install from https://developer.intuit.com/docs/0200_quickbooks_desktop/0100_essentials/quickbooks_web_connector
QuickBooks Version 18.104.22.168 minimum is recommended.
Once launched, the Web Connector looks like this. You can sync. anytime by clicking the checkbox to the left and then clicking "Update Selected".