From Satellite 6.8, we have satellite-maintain/foreman-maintain command available on capsule server to perform upgrade action. To simplify the Capsule upgrade process, we should allow upgrading capsule server via satellite using Remote Execution job template.
As far as I know this should already be done
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (Moderate: Satellite 6.9 Release), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2021:1313