The following are the necessary steps:

  1. Edit the donation form
  2. Go to step 3, Design Donor Screens
  3. Click Edit next to the Donation Form
  4. Select the custom field in question from the left column and click Edit
  5. Include possible responses in box (labeled "Responses")
  6. Click Apply
  7. Highlight the custom field
  8. Click add
  9. Click Save Order and Edit Selected