Bulk update displayname attribute to match cn attribute for all AD groups
Using the Microsoft Powershell commands you can do this. You need to import the AD module if you do not have it already imported into your current powershell session.
Get-ADGroup -filter * -Properties Displayname | Where-Object {$_.displayname -eq $null} | ForEach-Object {Set-ADGroup -Identity
$_ -DisplayName $_.SamaccountName}