This is a difficult part 4 inches from the bottom crease and open with your index finger to make a triangle shape on both sides. Please follow me.
About 4 inches from the bottom put your finger in to make a point ( Both sides ) left and right the same triangles.Fold elch side over the center line. Apply glue to thess triangles and fold in . Glue thess triangles here. Now fold the overlap, lean up extra glue , and press well. And stand your bag.