Step 1:
The other side of this paper is white,
prefold in half over this line.
Then turn the paper.

Step 2:
Valley-fold over these 2 lines

Step 3:
Mountain-fold over the line below and
valley-fold over the upper line.
Then turn the model.

Step 4:
Mountain-fold over the line on the left and
valley-fold over the line on the right.

Step 5:
Turn the model again

Step 6:
I opened the model a little for this step.
Push the corner indicated by the arrow
to the left by making an inside reverse
fold over these 3 lines.

Step 7:
Repeat step 6 on the left, see pink arrow.
Then close the model again by making
a valley-fold over this line.

Step 8:
Valley-fold over these 2 lines.
Then turn the model again.

Step 9:
Make an inside reverse fold over these three lines
(=valley-fold over the line in the middle and
a mountain-fold over the 2 outer lines).
Make these folds over the upper paper layer only.

Step 10:
Mountain-fold over these 2 short lines.

Step 11:
Open the model from below, see arrow,
and mountain-fold over this line. Fold
over the upper paper layer only.

DONE!