Change WooCommerce order confirmation text in

woocommerce-functions.php

<?php

add_filter( 'woocommerce_thankyou_order_received_text',  'my_custom_order_received_text' );

function my_custom_order_received_text() { ?>
	<div class="order-received-text">
		<h5>Your Order Was Successful!</h5>
		<p>Congratulations and a huge thank you for registering with us!</p>
		<p>You will receive a confirmation email shortly. If you have questions, please do not hesitate to <a href="/contact">contact us</a></p>
		<p>Thanks again!</p>
	</div>
<?php }