Hello NotMystical,
If you remove the other side of your AirPods from the case, and try playing a sound again, are you able to hear the sound from the missing one? If you still can't find it, you have the option of getting a replacement:
Replace a missing AirPod or charging case
If you still can't find your AirPod or charging case, or if something is damaged, get the serial number and then contact Apple Support for a replacement. Then learn how to set up your replacement.
Have a look at the link posted in the previous response for more information.
If you need further assistance, you'll want to reach out to Apple Support directly. They're best-equipped to take a closer look and provide some additional guidance. This link will help you get started: Contact - Official Apple Support
Take care.