Set agent or gateway failover servers

This will setup an agent or gateway server to use a specified primary management server and failover server.

Agent

$Agent = Get-SCOMagent -Name "FQDN"
$PrimaryServer = Get-SCOMManagementServer -Name "FQDN"
$FailoverServer = Get-SCOMManagementServer -Name "FQDN"
Set-SCOMParentManagementServer -Agent $Agent -PrimaryServer $PrimaryServer
Set-SCOMParentManagementServer -Agent $Agent -FailoverServer $FailoverServer

Gateway

$GatewayServer = Get-SCOMGatewayManagementServer -Name "FQDN"
$PrimaryServer = Get-SCOMManagementServer -Name "FQDN"
$FailoverServer = Get-SCOMManagementServer -Name "FQDN"
Set-SCOMParentManagementServer -GatewayServer $GatewayServer -PrimaryServer $PrimaryServer
Set-SCOMParentManagementServer -GatewayServer $GatewayServer -FailoverServer $FailoverServer

Add below line if you get this error: "The failover server xxx cannot be the same as the primary server."

Set-SCOMParentManagementServer -Agent | $GatewayServer FQDN -FailoverServer $NULL