How can I customize the Donation Tiers product image and text in cart?

To customize the donation product image and/or text, first go to the donation product:

If you have more than one donation product under Products, know that the donation type for the Donation Tiers donation product is "flat-donation."

Then, replace the default image with your own custom image:

To add custom text, scroll lower on the page to Variants and you'll be able to edit the text for each donation you've pre-set as well as for the custom donation amount (note that the variant showing cents is the one for when a customer enters a custom amount):