Power-shell distribution list update Managedby with foreach loop

Question

The script function is to find a user that is listed a a manager/owner on a distribution list and then replace that manager. The issue is I'm unable to replace the manager when they are a owner/manager of multiple distribution list. The script is successful
if I remove the foreach loop and just run the script on one distribution list. Please see error message below. Any help is appreciated. 
$user = "eharris"
#$DLSimilarmgr = "harris, aaron m"
$username = (get-aduser $user).name
$listDLgroup = get-distributiongroup -resultsize unlimited | where {$_.managedby -like "*$username*"} |fl name
$Foreach ($GrpDL in $listDLgroup) {
   $listDLManager = $GrpDL.ManagedBy 
   $NewDLManager = get-user -id "aharris"  
   $listDLManager+= $NewDlManager 
   set-distributiongroup $GrpDL -managedby $listDLManager -BypassSecurityGroupManagerCheck
Aaron Harris ExchangeSharePointGuy

Answer 1

Having issue combing the two scripts. The first scripts gets the DL managers. The second script will update the managed by field of the users and the previous managers of the DL. However, I don't know how to update a multiple DL when the user is listed as
a manager of more than 1 DL at a time. In script 2 I would like to update the multiple return value for script 1. Any help would be appreciated. 
#script 1 list the dl's the users is a manager of 
$user = "eharris"
$username = (get-aduser $user).name
$listDLgroup = get-distributiongroup -resultsize unlimited | where {$_.managedby -like "*$username*"} |fl name
#Script 2 working gets the dl and adds the new member and the previous members of that DL
$GrpDL = Get-DistributionGroup -id "#365DLTest"
$listDLManager = $GrpDL.ManagedBy $NewDLManager = get-user -id "eharris" 
$listDLManager+= $NewDlManager set-distributiongroup "#365DLTest" -managedby $listDLManager -BypassSecurityGroupManagerCheck
Aaron Harris ExchangeSharePointGuy