Command to read data off csv file for powershell

Hi,

I found this ps1 script off a web site where it will remove deleted AD users from user information list in SharePoint.  Trouble is I want the command to read off a csv file under column called "UserName" which will contain AD accounts.  Secondly, I want the append a domain prefix in front of user accounts via the script.  So within the csv under UserName column, it'll be something like jsmith, jjones.  I want the script to pass on domain\jsmith, domain\jjones and procedd withh the deletion.

Please advise.

Script I'm using is:

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue
 
#Define the Array with List of Users
$Users =@('ME\JamieT', 'Corp\EinstinS', 'Global\MarcM')
 
#Get all Site Collections
$SiteColl = Get-SPWebApplication "https://www.testsite.com" | Get-SPSite -Limit All
 
#Iterate through all Site Collections
foreach($site in $SiteColl)
{
 #Iterate through the users to Remove
 foreach($user in $Users)
 {
   #Check if User Exists in Site
   if ($Site.RootWeb.SiteUsers | Where {$_.LoginName -eq $User})
   {
      $Site.RootWeb.SiteUsers.Remove($User)  #You can also use: Remove-SPUser cmdlet
   Write-Host "$($user) has been Removed from $($Site.RootWeb.URL)"
   }
  }
}