To unset a CMake property, you can use the UNSET command followed by the name of the property you want to unset. For example, if you want to unset the property MY_PROPERTY, you can use the command UNSET(MY_PROPERTY). This will remove the property from the CMake cache and reset it to its default value. If the property was previously set with a value, unsetting it will revert it to its default behavior.