You can click on the link below to know about all the contests which can help you win a free trip against your credits https://www.tripoto.com/travel-for-free-contest , once you are at the link simple click on the contests you are eligible for and redeem your credit points.
There is something known as credit reedeming opportunities you can see there the amount of credits require and then reedem those credits to avail the trips. The trips will be listed there