Same species, same sex are often not very compatible. Sometimes as well, it takes some time for opposite sex to get a long well, as one might be ready to breed and the other not. With out any other cichlids to direct it's aggression towards, all of its aggression is directed towards the one cichlid.
Introduction can be accomplished by temporarily removing the fish for a couple hours ( such as placing your jewel in a 5 gallon pail with a towel over it to prevent it from jumping out). Then re-arrange the decor completely and introduce 5-6 tankmates at once before putting your jewel back in, after a few hours, once the new fish have somewhat settled in. I would suggest choosing 3 smaller cichlids as tankmates, from the following: 1 kribensis, 1 female convict OR 1 firemouth, 1 blue acara, 1 blockhead cichlid, 1 festivum.Choose 2-3 non- cichlids: 1 blue gourami, 1 CAE and/or BN pleco, maybe 1-2 zebra or giant danios. If any fish should get picked on excessively over time, removed it and return it to the LFS.
Another option, if you are wanting to breed jewels, is to purchase another 3 -5 jewels, of course introduce tthem before using the same method. Once a pair forms, remove the extras and return to the LFS.