Tableau Bridge is required to setup scheduled refreshes for AIO Tableau Connector inside Tableau Online
Please refer to the link and the video below for more details
Use Tableau Bridge to Keep Tableau Online Data Fresh
Download and install Tableau Bridge from this link: Tableau Bridge
After the installation is complete, Sign in to Tableau Online account from Tableau Bridge
Tableau Bridge client icon will appear in Windows System Tray
Publish the Tableau workbook to Tableau Online
In Tableau Desktop, go to Server > Publish Workbook
Click “Tableau Online”
Login to your Tableau Online account
Click Edit next to Data Sources
Select, Publish type: Published separately, Authentication: Embedded Password
Publish the workbook
Login to Tableau Online and navigate to the published workbook.