This is what helped me work around my issue. I was recently in South Korea and had my clock set accordingly. My main hard drive hadn't had enough space to download a graphics card update so I had deleted a bunch of the Microsoft apps I don't use, including the maps app.
I followed a previous comment about enabling location services. That at least got my computer to realize I'm no longer in South Korea, but decided I was in CST instead of EST and still wouldn't let me manually change the time zone. I tried re-installing the maps app and setting a default location to an EST city but that did nothing for me. After seeing this comment I went back to location services, turned on "allow apps to access your location" and then under "choose which apps can access your precise location" I enabled it for maps. With that enabled, it still didn't auto-correct itself to EST (with or without the default location set in the maps app) BUT it did make the option to manually adjust my time zone accessible again. So I set it to EST and then disabled location services again.