Snippet to replace "Add to Cart" with "Download" button on WooCommerce product page if logged-in customer has purchased downloadable product

replace-cart-button-with-download-single.php

<?php

// IMPORTANT: Add customer_has_download() function from here - https://gist.github.com/jorpdesigns/d155eaf0fe3260b0f59d514cca5004ed

add_action( 'template_redirect', 'product_single_download_button_check' );
function product_single_download_button_check() {
	if ( customer_has_download( get_queried_object_id() ) ) { 
		remove_action( 'woocommerce_single_product_summary', 'woocommerce_template_single_add_to_cart', 30 );
		add_action( 'woocommerce_single_product_summary', 'product_single_download_button', 30 );		
	}
}

// Create product_download__single_button() function
function product_single_download_button() {
	global $product;
	$user_id = get_current_user_id();	
	$downloads = wc_get_customer_available_downloads( $user_id );
	
	foreach ($downloads as $download) {
		if ( $download['product_id'] === $product->get_id() ) {
			echo '<a href="' . $download['download_url'] . '" class="button alt">Download</a>';
		}
	}	
}

?>