I received this in an email. You might also be able to find it in the promotions section of your account.

Earn 5,000 Rapid RewardsŪ bonus points when you register, and then book and fly two round trips (or four one-ways) revenue flights between January 27 and May 31, 2021. If a Member books and flies more than two round trips during the promotional period, Member will still only receive a one-time 5,000 Rapid Rewards bonus points. To register for this promotion, you will need to provide your Rapid Rewards account number at the time of registration. If you do not have a Rapid Rewards account number, you may enroll for free. Once you complete and submit the enrollment form, you will be automatically registered for this promotion if all eligibility requirements are met. Member must register for this promotion between January 27 and May 31, 2021 and registration must be completed prior to commencement of travel. Member's qualifying flight(s) must be booked through Southwest AirlinesŪ between January 27 and May 31, 2021 for travel between January 27 to May 31, 2021. Member's flight(s) must be completed between January 27 to May 31, 2021.