Recently bought left AirPod won't work

Hello,

Try this:

Go to Settings > Accessibility > Audio/Visual and scroll down to “Balance L vs R” (Adjust the audio volume balance) and make changes.

If no help, these are some general steps:

1) Try cleaning it: How to clean your AirPods and EarPods

2) See this: How to Fix Connection Problems with the AirPods

3) Full reset: Reset your AirPods

4) Service: AirPods Service and Repair

Good luck.