the paper I provided above (Zone 2 and heat - #25 by WindWarrior) has a list of protocols, for example self-paced:
or constant workload
For myself, I don’t worry, just go out and ride by perceived exertion. In the Saturday workout I posted above (Zone 2 and heat - #14 by WindWarrior) you can see as the temperature drops I increase power while still keeping HR well below normal for such a ride.
My garage hits 90+F and I’ve used the trainer with 2 fans and 3 fans. I’ll modify workouts if necessary. Last week I did some 30-sec jobbers outside in the heat, followed by a shorter threshold interval - that was a ‘heat friendly’ workout format. These days I just go outside and ride, however where I live outside is time-efficient, and better cooling.