It's rarely the actual diode which failed. It's normally a part of the driver circuit. So you need to non-destructively disassemble the device (quite challenging in a lot of designs), then have at least basic EE skills and tools to diagnose what is actually going wrong, and then once again some basic soldering skills.

> A bag of bulk LEDs imported from China is surprisingly cheap.

Like a lot of repairs it's not the parts that cost it's the time of even somewhat skilled local labor to repair.

Don't underestimate the ability to make it very difficult to non-destructively reach the actual LEDs in many of these devices in the name of being small or "stylish."