If you are on a smart trainer that is ERG enabled, and would like to disable it, there is a selector on the workout menu just above the ‘Workout’ button labeled ‘Use ERG mode’ - deselect it to give yourself a flat resistance during the workout. If you do not see this option, your trainer is not ERG enabled.
To adjust the resistance in a workout when not using ERG mode, select the workout and start riding. Once the workout has been started, there are two ways to adjust your resistance. First, you can use the Zwift Mobile Link app - four workout specific buttons appear on the actions screen when a workout is active (pause, skip block, and the two resistance adjusters). Alternately, you can use the ‘+’ or ‘-’ keys on your keyboard to adjust the resistance. When you adjust the resistance, a bar will appear to the right side of your workout HUD that shows your relative resistance level. The lowest setting is equal to flat road, while the highest is around an 8% grade.
And finally, the Elite RealPower is a smart trainer, and it is possible to create a workout that uses both ERG and SIM mode in its duration - the free ride block in workouts use SIM mode! However, it does not follow the gradient of the course, but rather gives the adjustable flat resistance that non-ERG workouts use. We currently have no plans for allowing a user to switch between the two while working out, but with the workout editor it would be possible to build a custom workout which utilizes both modes.
I hope this helped! Ride on!