Explanation:

Note:
Set-DatabaseAvailabilityGroup
The Set-DatabaseAvailabilityGroup cmdlet enables you to manage DAG properties that can't be managed from the Exchange Administration Center (EAC), such as configuring network discovery, selecting the TCP port used for replication, and enabling datacenter activation coordination (DAC) mode.
Parameters include:
/ DatacenterActivationMode
The DatacenterActivationMode parameter specifies whether datacenter activation mode is disabled (Off) or enabled for the DAG (DagOnly).
/ WitnessServer
The WitnessServer parameter specifies the name of a server that will act as a witness for the DAG. The server specified can't be a member of the DAG.
/ AlternateWitnessServer
The AlternateWitnessServer parameter specifies the name of an alternate server that's used to store file share witness data. The specified server must not be a member of the
DAG that's configured to use it. This parameter is used only as part of a datacenter switchover process. If the DAG is extended across multiple datacenters in a site resilience configuration, we recommend preconfiguring the alternate witness server and directory.