Step 2 - if you succeed give it a final rinse and spin dry ie, no detergent and no wash cycle.
Step 3 - take it out and look at it. If it's patchy wet a wash isn't going to work; if it's evenly damp it means the water has penetrated properly so you should be able to give it a wash.
I should have added - we wash our sleeping bags in our machine but I'm not sure how the bulk will compare to your duvet. The machine looks very full with each single sleeping bag but they do wash properly.