Here the 1849 LDS edition inserted an of in the phrase “the city Mulek”, giving “the city of Mulek”. The LDS text has retained the intrusive of. Elsewhere in the text (from Alma 51:26 through Helaman 5:15), there are nine instances of “the city of Mulek” and three of “the city Mulek”. As with all city names, either reading is theoretically possible, so here in Alma 53:6 we follow the earliest textual sources, including 𝓞, which lacks the of in “the city (of) Mulek”. A couple of times in 𝓟, Oliver Cowdery accidentally omitted the of in the phrase “the city of Mulek”; for discussion, see under Helaman 5:15.
Summary: Restore in Alma 53:6 the shorter form “the city Mulek” since this is the reading in both manuscripts as well as in the early editions.