Hi Abhishek,
Once your discount code has expired you have to obtain a new one using whatever program is currently available. So if there is an upcoming Virtual Training Day that provides discount code you would need to attend in order to qualify for discount.
For questions related to exam discounts/vouchers, you may create a free Certification support request:
https://aka.ms/credentialssupport
Creating support request screen should appear similar to below. You may need to select different options depending on your needs:
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP