change-promo-code-labels.php

<?php

// Do NOT include opening PHP tag above (<?php)
// Add to:
// - functions.php in child theme
// - Code Snippets
// - Settings > CheckoutWC > Premium Features > PHP Snippets (for Growth and Developer plans)

add_filter( 'cfw_promo_code_mobile_heading', function() {
	return __( 'Coupon code', 'checkout-wc' );
} );

add_filter( 'cfw_promo_code_label', function() {
	return __( 'Coupon Code', 'checkout-wc' );
} );

add_filter( 'cfw_promo_code_placeholder', function() {
	return __( 'Enter Coupon Code', 'checkout-wc' );
} );