It is important for all pilots, including Certified Remote Pilots, to keep their aviation knowledge up to date. If you have a Remote Pilot Certificate, you are required to have completed one of the following within the previous 24 calendar months to operate UAS under part 107:

• Pass the initial (Unmanned Aircraft General or UAG) or recurrent (Unmanned General Recurrent or UGR) knowledge test. You must be able to show a copy of your initial or recurrent knowledge test report if requested by the FAA as proof of currency.
• If you hold a part 61 pilot certificate and have a current part 61.56 flight review, complete the Part 107 Small Unmanned Aircraft Systems (small UAS) Recurrent online training course. You must be able to show a copy of your recurrent Certificate of Achievement if requested by the FAA as proof of currency.

Above is from the FAA website

Here is the course you must complete