Unfortunately, it is not possible to upload our workouts to your Tacx indoor trainer as Tacx does not allow any third-party apps to integrate with their systems. Maybe this will change now that Tacx is owned by Garmin, but for the time being, we have to live with this frustrating state of affairs.
The only option is to use an app like Zwift, Rouvy etc. If you have time to spare, manually recreate the JOIN workout for your Tacx.
We have launched an in-app workout player for Apple devices and in the process of building our own in-app Workout player for Android devices.