I can tell you stories about getting my 2 cats together! Yikes! LOL But, alas...after 6 months of patience and working with both of them, they get along great. Looking at them now you wouldn't even imagine that they didn't get along at first! I was lucky that my cat had such a laid back personality when he was brought in to meet my husband's cat. I tell you what, I've never heard a louder set of lungs on an animal! My husband's cat sure cat reach the earsplitting decibals!!! Some of the tactics to use are to spend time with each cat (separately). Speak calmly to both cats. Get something that has each of the cat's scents on it, like a towel they sleep on. Bring those things into the opposite cat's room to familiarize each to the other one's scent. Have brief interactions with the 2 cats. Start out at viewing from a distance and work your way up to having both in the same room at the same time (hands free). For a long time we couldn't do this, so we inserted a separate tactic. I would put one cat in a carrier (they feel safe there) and I would have one cat out and would be holding him. Then we'd switch and do the same thing with the other cat. Putting each cat in its own carrier and facing them toward each other also helped get my husband's cat adjusted to my cat. Thank goodness he was so calm!!! He didn't once raise a fuss when my husband's cat was yowling and spitting and growling at him!!
But, like Spencer said, isolate them and be patient. It could take some time. Good luck! Keep us up to date on what happens

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"In a cat's eye, all things belong to cats." - English proverb