Once the coupon is ready, only two sections can be modified: Redemption limits and Content. You can't edit the Coupon Code title, redemption times, the percentage/rate areas. If you need to make more changes, you'll want to recreate a new coupon.
The Redemption limits can be changed entirely. However, the Content section can only be modified very minimally:
If you have chosen All, then nothing can be changed.
If you have selected Subscriptions, you can only change what subscriptions it will be applied to.
If you have chosen Bundles, then you can switch which bundles the code applies to.
If you have selected Content, then you can choose what content will the code be applied to.
To edit a coupon, navigate to the Marketing tab and click on Coupons.
Choose the coupon you want to edit, click on the 3 vertical dots (⋮) and select Edit. Then make the changes to either what subscriptions, bundles, or content will the coupon be applied to or change the Redemption limits section to change expiration dates and limit redemptions. Lastly, click on Submit after editing.