Adjust your seat pan forward and backward (if possible) to ensure there is no chair contact with the back of your knees when your low back is in contact with the backrest. The goal is to ensure there is no contact stress from the seat pan but back support is maintained. Ideally, you should be able to fit one (1) or two (2) fingers between your knee and the seat pan.
AND
Adjust the angle of the seat pan to either level with the floor or slightly angled backwards towards the backrest.