41.

Apply the valley-fold of the step #40.

You've just completed a flap-folding on 1st flap.

You can repeat the step #39-41 to all four flaps.

Here I will show one more flap-folding for the 2nd flap.

Then you will have no problem applying the flap-folding for 3rd and 4th flaps.

Prepare to unfold the 2nd flap along the black dash line shown on the left picture.

42.

Unfold the 2nd flap.

Prepare to valley-fold.