You have to register for this promotion here. It looks like through February 28th, 2019, you can earn a free day reward everytime you rent twice for a minimum of 2 days (max 10 rewards.)
Avis Rent 2x Get Free Rental Day
Now through February 28, 2019, Avis Preferred® Members can earn Rental Day Rewards! To earn your rewards, rent twice for a minimum of two days. You can earn up to ten total Reward Days.
Plus, if you’re opted into Avis Preferred Points, you’ll earn points for every dollar you spend!
Not a Preferred member? Learn more and enroll today.
If you rent cars often, this could be a good promo for you!