Change heading for "Expires:" column in the WooCommerce Memberships My Account members area.

functions.php

<?php
// Only copy opening php tag if needed

/**
 * Change heading for "Expires:" column in the WooCommerce Memberships My Account members area.
 *
 * @param array $columns Array of columns to display in membership area.
 * @return $columns
 */
function sprucely_rename_membership_end_date_column( $columns ) {
	$wcm_columns  = $columns;
	$new_end_date = array( 'membership-end-date' => _x( 'Expires', 'Membership end date', 'woocommerce-memberships' ) );  // Change Expires to whatever you want.

	$columns = array_replace( $wcm_columns, $new_end_date );
	return $columns;
}
add_filter( 'wc_memberships_my_memberships_column_names', 'sprucely_rename_membership_end_date_column' );