$list = Get-Content "distributiongroup.txt"

Foreach ($i in $list) {

  $i

  $grp = get-distributiongroup $i

  $manage = $grp.managedby

  $newuser = get-user USER

  $newmanage = $manage + $newuser

  Set-distributiongroup $grp -managedby $newmanage -bypasssecuritygroupmanagercheck

}