Buy Now Button – Variation

add_filter( 'gettext', 'customizing_product_variation_message', 10, 3 );

function customizing_product_variation_message( $translated_text, $untranslated_text, $domain )

{

if ($untranslated_text == 'Select options') {

    $translated_text = __( 'Buy Now', $domain );

}

    if ($untranslated_text == 'Select options') {

    $translated_text = __( 'Buy Now', $domain );

}

return $translated_text;

}