Using JWT to retrieve and update User Profile's Info

I created a ReactJS web app with a “user profile” page where the logged user can save: name, surname, email and address. For the moment, every time I log-in and save the data a new object is created.

I would like each logged user to be linked to a single ID, namely Auth0 one, so that I can always retrieve and update the row of the right user in my MySQL database.
I read this Guide everything works without problems. Now how can I use JWT to make sure that every row in my database is only retrieved and updated by the right user?

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