How can I remove discount codes after customers exit the checkout?

I’ve noticed that when customers add a discount code on the checkout page and after getting back to the store and opening checkout again Shopify saves the applied discount code. How can I delete discount codes when customers leave the checkout?

Shopify Discount code is always the one generated, even if the customer uses the discount code the first time and still knows the combinations, he/she can still use it again, but there is a way to fix that.