title: How to change TextField value without having to delete it first (Flutter)
body: <p>I am trying to make a Phone Verification input field with six digits, all having max length of 1 digit.
  My issue is that I want the user to be able to change the value they entered without having to delete the old value. For example, the user typed &quot;2&quot; to a box, and when they clicked the box and typed &quot;3&quot;, the value should change automatically.</p>