Is there any drives/nas that both source and target servers can see? If yes then create a backup on the primary server to that drive, then once complete start the restore on the secondary server.
If there is no drive that both servers can see , then you have to backup on the primary server, copy the backup file to a drive which secondary server can see, for that file transfer you could use robocopy etc and once that's complete start the restore process.
HTH