Add this code to your child theme’s functions.php file:

add_filter( 'wpcargo_package_fields', 'wcp_custom_wpcargo_package_fields', 10, 1 );
function wcp_custom_wpcargo_package_fields( $package_fields ){
    /* Change fields to text */
    $package_fields['wpc-pm-qty']['field'] = 'text';
    $package_fields['wpc-pm-piece-type']['field'] = 'text';
    $package_fields['wpc-pm-description']['field'] = 'text';
    $package_fields['wpc-pm-length']['field'] = 'text';
    $package_fields['wpc-pm-width']['field'] = 'text';
    $package_fields['wpc-pm-height']['field'] = 'text';
    $package_fields['wpc-pm-weight']['field'] = 'text';

    return $package_fields;
}