JSFiddle - React, Tailwind, and code Playground

JavaScript

let str = `
$data= [
        'user_name' => 's',
        'user_place' => 'a',
        'address_list_code' => 's',
        'block_number' => 3,
]
`;

var regex = /'[a-z_]+' =>/g;
str = str.replace(regex, foundText => {
  return foundText.toUpperCase();
});
console.log(str);