変更のみ

Can I cancel my booking and be refunded?

No. We reserve the right not to refund passengers who cancel their tickets. You can change your flight only.

How about the condition of changing flight for Nok Flexi Fare.

Be able to change flight and date at unlimited but the changing must be done within 90 days after the booking has been made.

Flexi Fareの場合ですが・・・・

AieAsia

Can I cancel my booking and get a refund?

Once your booking is confirmed, it cannot be cancelled and the payment you made is not refundable.

However, you can get a refund on airport taxes.
この程度は、ご自分でしらべましょね。そのほうが早いと思います。