Just FYI, Delta has a NEW form for service dogs on their planes, which replaces the OpenDoors form they were using for the last couple years:
It used to be that people with disabilities who had a service dog did not need any special forms to fly on planes. This fact changed a couple years ago, and now many US airlines require extra paperwork. For a while, Delta was using a service called OpenDoors, but they have switched to using an in-house form.
Note: Please be aware that after completing the form, Delta will reach out to you, and following their call, you will need to contact them to ensure your information is "linked" to your ticket. This step is essential for them to determine the flight on which the pup will be traveling.