In your discount code settings where you manage that specific code in Shopify, there is a ‘Promote’ section at the top that allows you to copy the discount code as a link to auto apply once clicked!

It’ll look something like - https://{shop_name}.myshopify.com/discount/{discount_code}

Hey @Favewriter,

Adding to @Spark Bridge Digital LLC’s awesome response, I would also suggest taking a look at our How to Add Link that Applies a Coupon Code to a Shopify Cart Help Center article which also has various link formats you can use depending on the situations. 

This topic has also been brought up previously and I think taking a look at them could also be helpful to review:

I hope this helps!

David