I have a list of folks and their DN from AD (I do not have direct access to that AD). Their DNs are in format:
$DNList = \'CN=Bob Dylan,OU=Users,OU=Dept,OU=
You can remove the first element with a replacement like this:
$DNList -replace '^.*?,(..=.*)$', '$1'
^.*?, is the shortest match from the beginning of the string to a comma.
(..=.*)$ matches the rest of the string (starting with two characters after the comma followed by a = character) and groups them, so that the match can be referenced in the replacement as $1.