The best PowerShell cmdlet to assign a specific session host as a personal desktop to a user is Update-AzWvdSessionHost.
Syntax Example
To directly link a user's User Principal Name (UPN) to the designated personal session host, you can run the following block:
$parameters = @{
ResourceGroupName = 'YourResourceGroup'
HostPoolName = 'YourPersonalHostPool'
Name = 'YourSessionHostVMName'
AssignedUser = '[email protected]'
}
Update-AzWvdSessionHost @parameters
Reference:
https://learn.microsoft.com/en-us/azure/virtual-desktop/configure-host-pool-personal-desktop-assignment-type