From another post... (vmware-vsphere-f24/replication-but-what-about-the-veeam-server-t23440.html#p120670
I'm assuming this procedure would be done at my Site B and would apply to the Veeam server only. I would still need some methodology to get the vCenter server across. Also, Site A and Site B have different IP address ranges...
1. start the replicated Veeam backup server manually
2. do other VMs failover using your DR Veeam backup server console (in this case you will be able to automatically run a failback procedure)
3. once source site is up and running, initiate a failback operation for all VMs except backup server
4. replicate latest changes occurred on the DR backup server to the HQ host (via replication jobs and replica mapping functionality)
5. start Veeam backup server on the main site via vSphere Client
P.S. you could avoid steps 1,4,5 if your backup server managing replication jobs was located on the DR site (recommended approach).