This is Elias from Shopify Support. I'd be happy to lend a hand with this!
Just to clarify, are you looking for a way to allow repeat customers to use the same discount code? Or, are you looking to incentivize customers after each of their purchases?
If you'd like to allow repeating customer to use the same discount code, you can create a unique discount code and apply the customer eligibility to each of them without setting a usage limit.
Alternatively, if you'd like to incentivize customers after each order, you can consider integrating a loyalty program for your store. This way, you can offer more rewards as repeating customers continue to make purchases on your store. If you need any help with third-party apps, you can always reach out to the developers through the contact information found in the Support section of their app pages.
I'd love to learn more about your business and the discounts you'd like to offer. Can you share more details of how you'd like to offer dynamic discount to repeating customers?