how to edit your offer email that's been sent to say 'last chance'?

Hi there @Lvst, 

While you can’t change an email after it’s been sent, I’d consider either sending another campaign to the   segment of users who didn’t use your coupon or creating a conditional split  in your flow if this message was a flow email to target these customers and ensure they user their coupons! These threads of customers who wanted to accomplish something similar will help get you started! 

Hope this helps!

-Taylor