Hey,
I just created my first run with Garmin coach, I uploaded it from the watch to the app, but it was'nt updated in the garmin coach plan.
Can someone please assist?


The run you did was not started as the scheduled workout. If not proposed automatically (normally it is), you have to select the workout from the activity menu » Training » Workouts » Benchmark Run. Alternatively you can also start it from the calendar on the watch.
BTW, personally I never tried a Coach workout on the treadmill, but do not see anywhere that it is not possible. First, I recommend starting the workout properly with another treadmill run, and if it does not work, try an outdoor run.
I have Venu, but I don't understand how to start the workout properly through the watch, I'm not doing it through the mobile app.
Every time I finish the workout I sync (Bluetooth) the watch with the mobile and then the activity is shown in the mobile app.