NewDetailToPreview

CModule::IncludeModule('iblock');
$res = CIBlockElement::GetList(Array(), array('IBLOCK_ID' => 28), false, false, ["ID", "DETAIL_PICTURE", "DETAIL_TEXT", "PREVIEW_PICTURE", "PREVIEW_TEXT"]);
while($ob = $res->GetNext())
{

    if(!empty($ob["DETAIL_PICTURE"]) && empty($ob["PREVIEW_PICTURE"]))
        $ob["PREVIEW_PICTURE"] = $ob["DETAIL_PICTURE"];
    elseif(!empty($ob["PREVIEW_PICTURE"]) && empty($ob["DETAIL_PICTURE"]))
        $ob["DETAIL_PICTURE"] = $ob["PREVIEW_PICTURE"];

    if(!empty($ob["DETAIL_TEXT"]) && empty($ob["PREVIEW_TEXT"]))
        $ob["PREVIEW_TEXT"] = $ob["DETAIL_TEXT"];
    elseif(!empty($ob["PREVIEW_TEXT"]) && empty($ob["DETAIL_TEXT"]))
        $ob["DETAIL_TEXT"] = $ob["PREVIEW_TEXT"];

    $el = new CIBlockElement;
    $arLoadProductArray = array(
        "PREVIEW_PICTURE" => CFile::MakeFileArray(CFile::GetPath($ob["PREVIEW_PICTURE"])),
        "DETAIL_PICTURE" => CFile::MakeFileArray(CFile::GetPath($ob["DETAIL_PICTURE"])),
        "PREVIEW_TEXT" => $ob["PREVIEW_TEXT"],
        "DETAIL_TEXT" => $ob["DETAIL_TEXT"],
    );
    $test = $el->Update($ob['ID'], $arLoadProductArray);

}