When you decline or cancel a request, the DVD will be removed from your Tower. If you want to offer the DVD again, you will need to repost it.
If you are declining because you are out of town or unable to mail any DVDs for some reason, you should be using the Vacation/Hold feature to put your Tower on hold--this will prevent incoming requests.
Log into SwapaDVD, go to My Account and click on the request.
Go to the "DVDs to Mail" tab in My Account and click on the transaction for the DVD.
If this is a request for a Wish Listed DVD you must cancel it yourself.