How do I check-in for Southwest 24 hours to check-in for your Southwest Airlines flight 24 hours in advance, visit their website or use the mobile app exactly 24 hours before departure. Enter your confirmation number and last name, then follow the prompts to complete check-in. Once checked in, you can print your boarding pass, have it sent to your mobile device, or receive it via email. This ensures you secure a favorable boarding position and are ready to board when your flight departs.