Cannot get second part of dragon door lock

I am at the puzzle with the dragon in front of the door to the demon's lair. I have found both parts of the lock and inserted the right hand part. The left hand part will not budge, I found it easily enough in the lower RH corner. I got this far before, with same problem. I uninstalled the game and had to restart it from the beginning when I reinstalled. I refuse to start again. I am playing on my ipad

It suddenly worked