Alter The WooCommerce Single Product Add To Cart Text

function my_woocommerce_product_single_add_to_cart_text() {
    return 'YOUR CUSTOM TEXT';
}
add_filter( 'woocommerce_product_single_add_to_cart_text', 'my_woocommerce_product_single_add_to_cart_text', 20 );

All PHP snippets should be added via a child theme's functions.php file.