This isn’t a common problem, but if you’re sure your graphic drivers have been updated, I’d still recommend reinstalling Zwift. That really is the easiest way to clear previously remembered settings and the install should re-detect your current screen resolution properly. You won’t lose any of your progress or items in the game.
Please uninstall Zwift through your Control Panel.
Before restarting your Dell, check your \Documents and \Downloads folders - if you see any directories named Zwift, delete them.
Afterward, please reboot your Dell.
Once your laptop had rebooted, please download a fresh copy of Zwift from our website and give it an install.
If you’ve already tried all that and it hasn’t worked, please let me know.