From the Shopify admin:
Go to Settings (bottom-left of the admin)
Select Checkout
Click “Customize” in the settings area
Important:
Changes made using the live (published) “Customize” button are applied to your storefront immediately.
Click “+ Add block”
Select “Coupon List”
You can optionally adjust the following settings:
Days to display alert
Enter the number of days before expiration.
If a coupon’s expiration date falls within this range, it will be displayed as “Expires in X days.”
If left blank, this alert will not be displayed.
Coupon list title
Edit the title displayed at the top of the coupon list.
Coupon list description
Edit the text displayed below the title.
Login required message
Change the message shown before the customer logs in.
Edit note
Change the note displayed at the bottom of the coupon area.
Click “Save” in the top-right corner to apply your changes.
When a customer clicks “View more coupons”, a popup will appear showing the full list of available coupons.