SharePoint PowerShell that takes a list item that is a string and converts it to a number and then updates the list item.
$webUrl = "https://xxxx"
$listName = "Fleet Processing"
# Open web and library
$web = Get-SPWeb $webUrl
$list = $web.Lists[$listName]
$items = $list.items
foreach ($item in $items)
{
$Item["UIC_String"] = $Item["UIC_Num"].ToString()
$Item["UIC_String"]
$Item.Update()
}