1. Place the filter over the ventilate cover
2. Insert the fixed ring back on the inner side of the mask
3. Insert so that the gear-shaped is facing away from the outside of the mask
4. Insert the cover ring and the fixed ring so they fit alined
5. Place the cover ring and the fixed ring together
6.Rotate the fixed ring towards CLOSE to lock it
7. Flip the mask towards front and insert ventilate cover ring and filter
'a pury, your free'