Learn how to obtain an access token from Google needed for a WP plug-in

I have been attempting to install a backup plug-in on my website, but the installation fails. This is in the log: "Google Drive: ERROR: Have not yet obtained an access token from Google (has the user authorised?) (Invalid request (refresh token not present).) (no_refresh_token)." I do not understand what is needed or what to do to obtain the access token. I need someone who can explain and/or help me obtain the token so the plugin can be installed.