Many of us have asked for a pre-heat function on the Form 3. I’ve discovered a workaround for getting the Form 3 to preheat as desired.
Basically, the trick is to remove your build plate from the machine and start a print. Proceed all the way until it throws an error that you’re missing the build plate. If you open the machine and place your hand by the heater exhaust, you’ll feel that it’s blowing hot air. Leave the machine in this state for as long as you want to preheat the machine for.