How can I convert my pace-based workout in TrainingPeaks to be power-based?

It is very easy to convert TP pace-based plans to power but it depends on how the workout is set up. For example, this plan is based on a threshold pace that you can easily convert by switching to % Functional Threshold Power (your Critical Power). Select your workout in TrainingPeaks and open the workout builder by clicking on the graph of the workout.

Make sure that your CP is copied from the Stryd ecosystem to TrainingPeaks (it does not sync automatically). You do not need to worry about the zones. You find this setting under your profile in TraininPeaks (screenshot below):