How to backup and clear logs (truncate logs) on an AAG Database

I have read Microsofts steps but if a Copy-Only Backup is only supported in an Always On Group then how will the logs be cleared?

I have a primary and secondary server in an AAG configuration, I've read I can backup the secondary replica which will also clear the logs on the primary when the maintenance plan runs, but a copy only backup does not clear the logs as far as I know.

Please confirm what I am missing here so I can configure the backups to clear the logs,

Thanks