Go to Google Sheets and open the sheet you want to show.
Click on File.
Click on Share.
Click on Publish to web.
Click on Publish, then on OK.
Copy the generated link.
Go to the Management Console.
Click on the layer where you will add the Google Sheets document.
If the layer has no media, the apps dialog will open. Otherwise, click on Add New
Click on Google Apps.
Then click on Google Sheets.
Paste the link you just copied.
Click on Save.