Corrected Script and now it is working...

Add-PSSnapin Microsoft.SharePoint.PowerShell -EA SilentlyContinue

$web = Get-PnPWeb /sites/InterSignWorkgroup

$list = Get-PnPList "FWO History"

$items = Get-PnPListItem -List $list

foreach($item in $items)

{
$lookup = $item.FieldValues["FWO_x0023_"]

Set-PnPListItem -List $list -Identity $item -Values @{"Title" = $lookup}        

}

Corrected Script and now it is working...

Add-PSSnapin Microsoft.SharePoint.PowerShell -EA SilentlyContinue

$web = Get-PnPWeb /sites/InterSignWorkgroup
$list = Get-PnPList "FWO History"
$items = Get-PnPListItem -List $list

foreach($item in $items) {    
    $lookup = $item.FieldValues["FWO_x0023_"]
    Set-PnPListItem -List $list -Identity $item -Values @{"Title" = $lookup}        
}