Delta sends you an email and asks you to fill out electronically . I had done that 2 days prior to returning to US. When we arrived at the airport a Delta rep announced anyone who hadn’t filled it electronically could scan the big QR coded paper to fill out otherwise they wouldn’t be able to check in at the counter. He repeated this throughout the 45 minutes we were on line. I have no idea what people did who didn’t have a phone? There was no paper to fill out as we had in April.