Thanks for reporting this. First, does the same audio imbalance happen when you use the headphones on another device?
Windows normally shows the left and right balance under Settings, System, Sound, then Device properties, so if the option is missing, I recommend updating or reinstalling the audio driver through Windows Update or the device manufacturer. Once the driver refreshes, check the Levels tab again. If the balance still does not appear, test a different audio port or try another headset to confirm if the issue is hardware related. Let me know what model of headphones and connection type you use.