There is one question that keeps coming up among drone pilots. What do I do if my license (correctly known as a "certificate") expires? There is a very short answer: your remote pilot certificate does not expire. It is good forever. But even though it never expires, you must renew it every two years in order to continue flying under Part 107. That is done by taking an FAA written exam called the Recurrent Test. The renewal/recurrency period starts on the date of your last test and extends to the end of that month, two years later.
UPDATE, Feb. 8, 2021. Begining on March 1, 2021, you will no longer visit a PSI testing center for your Recurrent Test. It will be conducted online, for free, at www.FAASafety.gov.
The Recurrent Test is currently an abbreviated version of the initial knowledge test (but this will likely change in 2020). Instead of 60 questions, it only contains 40. Just like with the initial test, it is taken at an authorized testing center (https://faa.psiexams.com/faa/login) and costs $160. Don't get angry that this is a money grab by the FAA. The testing fee goes to PSI.
The second most popular question asks what happens if you, a Remote Pilot, go past the two-year period without taking the Recurrent Test? In this case, there is nothing to worry about. From the end of the 24th month, you simply may not fly under Part 107 until you have taken and passed the Recurrent Test. Take the test whenever you can to get current again, and you're good to go for the next 24 calendar months. Scheduling is done online but you can call PSI at (844) 704-1487 for assistance.
After you have passed your Recurrent Test, there is nothing more for you to do. You don't have to visit iacra.faa.gov. Just keep a copy (digital is fine) of your Knowledge Test Report with you to prove that you are current.