How to add Google+ Community queue
First, you'll have to download and install Friends+Me desktop application from https://app.friendsplus.me/teams/0/extension
The desktop app provides functionalities not provided by official Google+ API such as publishing to Google+ communities, person and hashtag mentions and also support for posting to GSuite Google+ accounts.
Sign in with your Friends+Me and Google account within the desktop app once installed.
Mind that the desktop app must be up and running at times your Google+ community posts are scheduled for. Friends+Me is not able to publish to G+ communities otherwise.
Next step is to go to the Friends+Me Web application page https://app.friendsplus.me/teams/0/accounts/add and connect your Google+ communities.