To update packages on an existing, inactive BE, mount BE first, in order to gain access to it, Then, you can update packages on it.
The beadm mount command mounts a BE at a specified mount point. The mount point, if it exists, must be empty. If the directory for the mount point does not exist, the beadm command creates the directory, then mounts the BE on that directory. However, it remains inactive.
If the specified BE is already mounted, the beadm mount command aborts.