As we cannot back up a secondary site, we need to recover a secondary site from a primary site. We can restore a secondary server from the Configuration Manager console. Right-click on the secondary site in Configuration Manager and choose Recover secondary site. Remember that there are a few of prerequisites that need to be in place in order to perform a successful restore:
The server to which we want to restore the secondary site server needs to have the same FQDN as the old server.
It needs to have the same security rights as the old server.
It should use the same installation path as the old server used.
It needs to have SQL Express installed before recovering. The SQL Express version needs to be the same as it was before and should have the same instance.