I am sorry to hear that your cichlid has not improved. You know your fish better than anyone, and you'll have to decide when he is not having the quality of life that he deserves, then you'll have to euthanize.
The most humane way is to put the fish in a bowl of water and place it in the freezer. Leave it in their overnight, and then in the morning plant the ice chunk in the garden.
It is never easy to make these decisions.