Left airpod does not work and I don't have an official case

Left airpod does not work and I don't have an official case

so I bought AirPods a while back, then my case broke and to save money (because the case is practically worth a new pair of airpods) I bought a 3rd party case on amazon. Randomly, a few weeks ago, the left earbud stopped outputting audio/being recognised. Any idea how to fix this WITHOUT buying the actual case for £80?

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