I have the same issue with a headset attached to a windows 10 computer. No volume controls available through the website. VERY frustrating (and honestly painful).
Please, there must be something besides switching platforms.
@rswitalski If you're using the web app or desktop app on Windows 10, then you will have individual volume controls for every app running currently, through the Volume Mixer (right-click the speaker icon in the task bar).
Those control have no affect on the headset volume for GoToWebinar on Windows 10 or in Zoom. They do control the speaker volume if I disconnect the headset.
However, I can control the volume of my headset if I am listening to an online class through Coursera (and other similar tasks).
OK, then it sounds like GoTo is not the only application affected by the problem. In your case you might want to check for audio driver updates available through the device manufacturer's website.