I tried running this command to change the destination, but it didn't seem to work. I thought that it might move the existing groups to the new location after the next sync.
$a = Get-ADSyncGlobalSettings
($a.parameters | where {$_.Name -eq "Microsoft.GroupWriteBack.Container"}).Value = "[new destination]"
$a | Set-ADSyncGlobalSettings
In order to change the destination, I had to: