OK here's pictures
Here's the model at the beginning of step 10, as pictured in the diagram. My thumb is on the front of the model as pictured in step 10, and i'm holding open the flaps on the top, you can see the point hidden inside.
This is opening up the sides of the model, my index finger is now on the front of the model as pictured in step 10. You can see I'm opening up the side and the hidden point is now visible.
Once you've opened up both sides as in the previous picture, you fold up the bottom points to meet the top of the model, as below. Do this on both sides
Now close up the sides again, returning the model to the configuration it was at the start of this process, with the flaps exposed at the front and back, but with the bottom points reverse folded up to the top.
Step 10 completed.
Hope this helps!