You'd have to reinstall to choose UEFI during install, then correctly boot the media as a UEFI device.
Using Legacy mode or CSM on a modern UEFI PC is like buying a new car and turning off all the safety features.
When ready to reinstall, I'd load Factory Defaults and then make sure it enables UEFI, disables CSM, enable Secure Boot and Fast Boot, allow only Windows Boot manager to remain first in boot Priority order - which may only be invoked during install when you boot UEFI media and clear the hard drive of all partitions to reset formatting.