>>624904
1. Focus only on the long vertical valley fold (cf. picture).
There will be annoying layers in the back, just don't mind them for now.

2. Next, insert a finger where indicated by the large arrow, and push gently the layers from inside, starting to form montain folds on the upper part.

3. Keep gently pushing, and with the other hand, control the mountain folds so that they align as expected.

4. And you are done (previously mentioned mountain folds are in blue; the red line should be on the center crease line or so).
Well, almost done, because you need to do the same on the right.

Hope it helped a bit, but tell me if something is not clear!