I've been searching this online for a long time and I cannot find a solution. I saw one answer on this site suggest that logging into both acccounts on the device should merge them, but this is not the case, as that resulted in me having two accounts now, the facebook one is at level 1 and the king one (my main one) is at level 60. The King FAQ says to login to your King account on a web browser, but that functionality has been removed from the website.