If you find the swimming pool lights can not turn on, or flickering, you can start with some simple check first.
Firstly and the most important step is to turn off the power supply, and take the lamps out from your swimming pool lights Niche or from the wall of the pool.
Check if there is water inside the lamps, 80% of swimming pool lights failures are caused by the poor waterproof function, the water goes inside and damages the electrical parts.
If there is no water inside, probably the LEDs are burned or drivers are damaged with improper voltage input, or the wire connection inside was not made firm enough, they are loosened.
It is not safe for people to fix the swimming pool lights by themselves, at any time your pool lights fail, please contact a licensed electrician to fix them or send them back to the LED swimming pool lights supplier to fix.