So you want to send promotional offers and coupons to your current customer in WooCommerce

Here are 3 methods
1- Use a plugin to get past customers email address. You can use this one. free. ( then upload it to a email marketing platform (sendinblue, mailjet, mailerlite etc..) prepare a mail over there and send.
4. You can use mailchimp and woocommerce for mailchimp plugin. problematic and no support but anyways.