I just finished assembly on this plane last week and I am familiar with the area. If you take the horiz stab and lay it next to the covered block, you can just make out an indention in the covering. I just pressed into the covering with an X-acto. Do the same for the vert stab. The piece you need to remove is actually tacked in with a little CA. I had to run the blade of the X-acto between the two pieces before it would slide out.

Having said all this; once I had the filler piece removed, the space allowed for the horiz stab was too small and both fillets came loose. I took them off too and plan on gluing them in place at some point. I'm too busy flying the plane right now. Absolutely beautiful flying plane. I powered mine with the OS 91 Surpass II 4-stroke.

Hope this helps,

Brian