In order for the Analytics Edge Add-in to show Google Sheets files and folders in the Read Google Sheets or Write to Google Sheets function wizards, you need to associate the files and folders with the Add-in. This is done in the Google Sheets web interface by selecting the files and folders you are interested in, then right clicking and selecting Open With > Analytics Edge Add-in.
A browser window should open showing this page.
Returning to the Analyics Edge Add-in, those files and folders should now be visible in the Read Google Sheets and Write to Google Sheets function wizards.