unfortunately you can't! I have the same problem, i either sold it or threw it away earlier in the game, it's so stupid that you can find another one!
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Breed two azumarill's one holding a sea incense item once you obtain the egg and hatch you should get azurill if you don't you need to have ruby, sapphire or emerald do the exact same method as above to get azurill.
Route 204 which is right above Jubilife City. You have to go through a patch of grass to your left and surfacross a small pool of water. Once you get the incense, you can breed two marills ( a boy and a girl ) to get an azurill.
This might work: Give a sea incense to a azumarill then put it in the four island daycare with a ditto or another azumarill that is opposite gender from the other one, wait till the old man gives you an egg hatch it and its azurill. Didn't work? You may have to get one from ruby or sapphire or emerald.
you cant get another Sea Incense but you can get a Mystic Water it raises the power of water type moves
Route 204