It is not possible to reverse a coupon exchange. A coupon exchange is a "payment for ordered coupons with your own coupons". To reverse it would mean to also reverse the coupon exchange of all users whose transactions are connected to your coupon exchange by trading with them them, directly or indirectly. That can be tens of people, all of whom are happy that they got an exchange.
You can however adapt and cancel your coupon orders at any time before they become part of a coupon exchange. You can also cancel the parts of your coupon orders that have not yet become part of a coupon exchange. So simply make sure to cancel all unwanted coupon orders before the next coupon exchange happens.
Also, you can reverse the effect of a coupon exchange by offering the coupons you received but don't want. Somebody else may want them, and in exchange you get other coupons that you order.