Handle Map in React

Hi! I´m a beginner front end dev, and i have some work with react.
But i have a doubt with manipulate an element in a map render components.

The Problem

Change a msg variable in only one element in a map
So, i have this variable in a title element:

And when the button is pressed i call a function and try set the message in this way:

Obs: I use useRef hook to get el reference in the dom

So, anyone can help me with this?