Hello @Mark_Harris7, welcome to Zwift Forums! I recommend trying out @Stephen_Metcalfe ‘s method of reseting your preferences. It sounds like you may have manually disabled virtual shifting in the past, but resetting your preferences will re-enable virtual shifting by default and should allow you to set your gear range and shifting style.
If this doesn’t solve the issue for you, please don’t hesitate to reach out to us in Support!