#Let the user fill in their admin url, username and password

$adminUrl = Read-Host "Enter the Admin URL of 0365 (eg. https://<Tenant Name>-admin.sharepoint.com)"
 
$userName = Read-Host "Enter the username of 0365 (eg. admin@<tenantName>.onmicrosoft.com)"
 
$password = Read-Host "Please enter the password for $($userName)" -AsSecureString

$credentials = New-Object -TypeName System.Management.Automation.PSCredential -argumentlist $userName, $password
 
$SPOCredentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($userName, $password)
 
#connect to to Office 365
 
try{
    Connect-SPOService -Url $adminUrl -Credential $credentials
    write-host "Info: Connected to Office 365 Succesfully " -foregroundcolor green
 }
 
catch{
      write-host "Error: Could not connect to Office 365" -foregroundcolor red
     }

$siteUrl = Read-Host "Enter the Site URL"

$ctx = New-Object Microsoft.SharePoint.Client.ClientContext($siteUrl)

$ctx.Credentials = $SPOCredentials
$ctx.Load($ctx.Web.Lists)
$ctx.Load($ctx.Web)

 try
 {
   $ctx.ExecuteQuery()
   
  
   $_lists = $ctx.Web.Lists

   $_list = $_lists.GetByTitle("Documents")

    $qry = [Microsoft.SharePoint.Client.CamlQuery]::CreateAllItemsQuery()
    $items = $_list.GetItems($qry)

    $ctx.Load($items)

    $ctx.ExecuteQuery()

    Write-Host "Retreving Number of items : " $items.Count -foregroundcolor green

    foreach($listItem in $items)
	{
		Write-Host "Updating value for Lookup field"
	   
        $listItem["ProjectID"] = $listItem["TempProjectID"] # Update Field Value Here
        
        $listItem.Update();

        $Ctx.ExecuteQuery();

         Write-Host "Updated."


    }

  }
        catch
        {
            $ErrorMessage = $_.Exception.Message
         write-host "Error : " $ErrorMessage -foregroundcolor red
        }