change the primary address (prefix) distribution list group

IrvanR You could use something like:

#Install module and connect
Install-Module ExchangeOnlineManagement
Connect-ExchangeOnline

#Loop through csv file and change primary smtp
foreach ($row in Import-Csv -Path C:\data\dl.csv -Delimiter ';') {
    try {
        Set-DistributionGroup -Identity $row.GroupName -PrimarySmtpAddress $row.Email -ErrorAction Stop
        Write-Host ("Updated {0}" -f $row.GroupName)
    }
    catch {
        Write-Warning ("Error updating {0}" -f $row.GroupName)
    }
}

CSV looks like:

GroupName;Email
Testdl1;email address removed for privacy reasons
Testdl2;email address removed for privacy reasons