Updare Post

Hey

Actually am creating a form to update the post content.

What I did

1) created a form for update post
2) loaded the post content into that form
3) on submit updated the content of that form

Issue :
On submit it also added one post , also updating the post.What I want it just need to update not added one more post.Here my code:

function update_post_from_car_submission() {

    // Get the submitted field values
    $post_title = af_get_field('car_name');
    $post_content = af_get_field('car_description');
    $post_img2 = $_POST['acf']['field_5a8a3a9a526e3'];
    $upostid = af_get_field('field_5a924b672a753');

    $model = af_get_field('selected_car_model_is');
    $price = af_get_field('price');
    $variant = af_get_field('selected_variant_is');
    $make = af_get_field('selected_car_make_is');
    $type = af_get_field('type');
    $fueltype = af_get_field('fuel_type');
    $gallery = af_get_field('gallery');
    
    $year = af_get_field('year');
    $post_data = array(
        'ID' => $upostid,
        'post_type' => 'cars',
        'post_status' => 'pending',
        'post_title' => $post_title,
        'post_content' => $post_content,
    );
    $post_id = wp_update_post($post_data);

    if ($model) {
        update_field("field_5a6bf9b634f71", $model, $post_id);
    }
    if ($make) {
        update_field("field_5a6c5e6198059", $make, $post_id);
    }
    if ($price) {
        update_field("field_5a59be8db2240", $price, $post_id);
    }
    if ($variant) {

        update_field("field_5a6c36711836b", $variant, $post_id);
    }
    if ($type) {
        update_field("field_5a64b0c1a2e8e", $type, $post_id);
    }
    if ($fueltype) {
        update_field("field_5a6c3bc55ee8f", $fueltype, $post_id);
    }
    if ($gallery) {
        update_field("field_5a59be8db22c3", $gallery, $post_id);
    }
    if ($year) {
        update_field("field_5a59be8db21c6", $year, $post_id);
    }

    if ($post_img2) {
        update_post_meta($post_id, '_thumbnail_id', $post_img2);
    }
}   

add_action('af/form/submission/key=form_5a89c16a59701', 'update_post_from_car_submission', 10);

Also tried acf/save Still same issue.

So what I need to use so that it just update the value not create one new.