How to redirect to a page after submitting form data?

Form handling needs to happen in functions.php (or equivalent) so that it triggers before headers are sent. Here is the how I achieved redirection after form submit:

add_action('init', 'redirectAfterSubmit');

function redirectAfterSubmit() {
  if (isset($_POST["submit"])) {
    insert_row();
    wp_redirect( "/thank-you", 301 );
    die();
  }
}

function insert_row(){
  // form handing here
}