Create custom add to cart in WordPress

Use woocommerce_add_cart_item_data and woocommerce_add_order_item_meta filters. Wrap all your input fields inside product form( I assume that those tabs are made with javascript so there is no need of reloading the page for each one’s content) and set that form’s action to add to cart url

Use this in your custom template

$product = get_product(77);
echo '<form method="POST" action="' . $product->add_to_cart_url() .'"> elements here, including quantity </form>';