How to Update Data in WordPress Database Using PHP with MySQL?

Question

I want to send a RTR to our candidate, so I have made a form using Contact Form 7 plugin to fill up the form by myself & when I filled the form, an email will send to candidate with two buttons approved and declined. I created a form like:

<label> Candidate Name
    [text* CandidateName autocomplete:name] </label>

<label> Candidate Email
    [email* your-email autocomplete:email] </label>

<label> Position
    [text* Position] </label>

<label> Company
    [text* Company] </label>

[hidden clientResponse "not received"]

[submit "Submit"]

Initially, the client response was set to "not received" when the client click on the "approved" or "declined" button, I want to update clientResponse to respectively "approved" or "declined". To do this I added these custom code in WordPress theme editor:

function custom_thank_you_content() {
    if (is_page('thank-you')) { // Check if it's the 'Thank You' page
        if (isset($_GET['response']) && isset($_GET['email'])) {
            $response = sanitize_text_field($_GET['response']);
            $email = sanitize_email($_GET['email']);

            if ($response == 'approved') {
                echo '<h2>Thank You!</h2>';
                echo '<p>We are thrilled to know you are interested. We will get in touch with you shortly.</p>';
                  
            } elseif ($response == 'declined') {
                echo '<h2>Thank You for Your Response!</h2>';
                echo '<p>We appreciate your feedback. If you change your mind, feel free to contact us anytime.</p>';
            }
        } else {
            echo '<h2>Thank You!</h2>';
            echo '<p>We appreciate your response.</p>';
        }
        exit; // End script execution to prevent the default page content from loading
    }
}
add_action('wp', 'custom_thank_you_content');

function update_customer_response($response, $email) {
    global $wpdb; // This brings the global $wpdb object into the local function scope

    $table_name = $wpdb->prefix . 'db7_forms'; // Accessing the table with the WordPress database prefix

    // Update the customerResponse field where the email matches
    $wpdb->update(
        $table_name,
        array('clientResponse' => $response),
        array('form_value' => $email)
    );
}

But the resesponse is not updating. What can be the reason and how can I achieve it?