You have the later version which does not have any pins holding the grip in place (the pins were notorious for splitting the wood, because of the stress placed on the grip when cocking). Getting the grip off the unpinned version is by no means obvious. You will first have to remove the trigger guard, and then behind the trigger there is a screw holding the grip to the frame. Once you have removed that screw you can slide the grip off along its key-way. The sear housing can then be accessed.
This thread might also be useful: https://www.airgunbbs.com/showthread...ghlight=Haenel
Hope this helps.