Understand String Immutability extra help

Tell us what’s happening:
hey guys so I asked for help on this yesterday and got a couple answers and nothing that really explained it well so If someone could break down what Im doing wrong and why and how to do it and then an answer…
Thanks guys

Your code so far

// Setup
var myStr = "Jello World";

// Only change code below this line

myStr[0] = "J"; // Fix Me

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Link to the challenge:

Strings are immutable, you can access a single character using bracket notation, but you can’t change it
It means that if you want to correct the spelling mystake, without changing the first line, you can’t do myStr[0] = 'H', but you need to do something else entirely to make myStr have a value of "Hello World" (remember, you can’t change single characters in a string using bracket notation, if you want to change the value in the variable you need to do something else)