qz app is the answer . check on youtube qz auto incline zwift 
Is auto incline with smart treadmills ftms in the works so that we don’t have to use a pass through app like QZ? If iFit can do this and we have auto incline with the zwift kickr it’s time to be added for runners also. Respectfully.
It does sound like it’s coming. See comments from Zwift in this Q&A:
Paul,
Thank you 
Best,
Dave