All prescribed workouts can be done as outdoor or indoor and there is no distinction in VeloPro between an indoor or outdoor workout. You may download workouts in ERG or ZWO format to be used with your indoor trainer.
Click on the workout in your plan and a box will pop up. From there you can download a Zwift file or an ERG file, which you can upload to your indoor trainer.
If you prefer to do shorter indoor workouts than what is prescribed, then simply do a shorter workout and the system will read that and adjust your plan going forward, if necessary.