By default, ContentSync will pull content from all of your spreadsheet sheets. Any new content pushed to your spreadsheet will default to the main sheet.
You can specify which sheet a layer is synced to within the ContentSync Layer Inspector. Look for the sheet customization icon:
Once toggled, the sheet customization field will appear and you can customize the name of the sheet you want to sync to:
Now, when synced, the content will appear on your customized sheet.