We created a video for better understanding how to connect the google sheet that you have already had in your Seller Assistant App account.
Log in your Seller Assistant App account.
Choose "Google Sheets" in the side menu.
Choose the one you want to save your data in.
Before connecting existed Google sheet make sure that:
you have permission to edit a table or sheet you want to connect;
the sheet doesn't have merged or protected cells
the sheet has free space.