I’d like to add a button under the “Add to Cart” button which says “Buy on Amazon” and links to my Amazon product page [closed]

You can copy this code to your functions.php and you will add a button under Add to Cart Button.

add_action( 'woocommerce_after_add_to_cart_button', 'content_after_addtocart_button' ); 

function content_after_addtocart_button() { 
    echo '<div class="content-section"><br><br><a href="https://www.google.com/"><input id="amazonBtn" type="button" value="Buy on Amazon"/></a></div>'; 
}

Change the Google link for your Amazon link.