Add A Button to WooCommerce Product Page

Please use the following code snippet. It’ll add a new button right after the add to cart button. The code is well commented, hope that’ll be helpful for you.

add_action( 'woocommerce_after_add_to_cart_button', function() {
    /**
     * If you need product data here you can set $product as global
     * then you can easily access product data through $product object
     *
     * global $product;
     */

    /**
     * You may have to build product customization link automatically
     * if the customization link follows same pattern and has product
     * id then you can store the customization product id in product meta
     * and retrive that meta using $product->get_meta( '_customization_id' );
     */
    $builder_product_link = 'http://builder.alltype.com/';
    ?>

    <a class="button" href="https://wordpress.stackexchange.com/questions/296423/<?php echo esc_url( $builder_product_link ); ?>"><?php esc_html_e( 'Customize Product', 'text-domain' ); ?></a>

    <?php
} );