If a card is declined with the decline code do_not_honor, the only way to resolve this is to ask your customer to reach out to their card-issuing bank to look at the transaction and determine why it was declined. Customers should provide the bank with the charge amount, date/time, and the company name for assistance.
Stripe is not given any additional information beyond the decline code and cannot provide insight into why the card was declined.
Declines (Stripe Docs)
Bank decline codes (Stripe Docs)