Magento update text attribute type to select

update.php

<?php
require "app/Mage.php";
umask(0);
Mage::init('admin', 'store');

$attrCode = 'model'; //your attribute code here
$attrId   = (int) Mage::getModel('eav/entity_attribute')->getIdByCode(Mage_Catalog_Model_Product::ENTITY, $attrCode);
$resource = Mage::getSingleton('core/resource')->getConnection('core_write');

try {
    $resource->beginTransaction();

    /**
     * Collect old products values
     */
    $collection = Mage::getModel('catalog/product')
        ->getCollection()
        ->addAttributeToSelect('sku')
        ->addAttributeToSelect($attrCode)
        ->addAttributeToFilter($attrCode, ['notnull' => true]); 
        
    $data        = $collection->getData();
    $productData = [];
    foreach ($data as $product) {
        $productData[$product['entity_id']] = $product[$attrCode];
    }


    $select = "select distinct value from `catalog_product_entity_varchar` where `attribute_id` = {$attrId};";

    $modelValues = $resource->fetchCol($select);


    /**
     * Change attribute type
     */

    $updateAttrType = "UPDATE `eav_attribute` SET `backend_type` = 'int', `frontend_input` = 'select', `source_model`='eav/entity_attribute_source_table' WHERE `attribute_id` ={$attrId};";

    $resource->query($updateAttrType);

    $deleteOldValues = "delete from `catalog_product_entity_varchar` where `attribute_id` = {$attrId}";


    $installer = new Mage_Eav_Model_Entity_Setup('core_setup');
    $installer->startSetup();

    /**
     * Add options to the attribute
     */
    $iProductEntityTypeId    = Mage::getModel('catalog/product')->getResource()->getTypeId();
    $aOption                 = array();
    $aOption['attribute_id'] = $attrId;
    for ($iCount = 0; $iCount < sizeof($modelValues); $iCount++) {
        if (!isset($modelValues[$iCount])) {
            continue;
        }
        $aOption['value']['option' . $iCount][0] = $modelValues[$iCount];
    }
    $installer->addAttributeOption($aOption);

    $installer->endSetup();


    /**
     * Update products with new data
     */

    $attribute = Mage::getModel('eav/config')->getAttribute(Mage_Catalog_Model_Product::ENTITY, $attrCode);
    $allOptions = $attribute->getSource()->getAllOptions(true, true);
    foreach ($allOptions as $instance) {
        $myArray[$instance['label']] = $instance['value'];
    }


    foreach ($productData  as $productId => $value) {
        if (!isset($myArray[$value])) {
            continue;
        }
        Mage::getModel('catalog/product_action')->updateAttributes([$productId], [$attrCode => $myArray[$value]], 0);
    }

    $resource->commit();
} catch (Exception $e) {
    echo $e->getMessage();
    Mage::logException($e);
    $resource->rollBack();
}