Hi RMF_AndyPlayz, I am Paulo and I'd like to help.
This can happen sometimes if manufacturers permanently lock the left-right audio channels of their accessories. You can try a registry tweak to disable the joint volume of your earphone's audio channel and see if you can adjust them independently once done.
- Windows key + R then enter regedit
- Navigate to this path
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Bluetooth\Audio\AVRCP\CT
- Double click on the value named DisableAbsoluteVolume and change its value data to 1.
- Click OK to save then exit and restart your PC
See if this works