Change the value of an element in a PFUser Object of type Array, in Swift

I'm new to Parse server. First, I create a multidimensional array as an object on Parse server

let day1 = ["one", "two", "three", "four"]
let day2 = ["five", "six", "seven", "eight"]

let jan = [day1, day2]
let feb = [day1, day2]

let calendar = [jan, feb]

let user = PFUser()
user.username = userNameTextField.text
user.password = passwordTextField.text
user["Calendar"] = calendar

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What I want is to be able to do a PFUser query and change the value of calendar [ 1 ] [ 0 ] [ 1 ] from "two" to "zero". I've gone over Parse's documentation, but I'm just confused on how I could accomplish this. Thank you for your help!