Flush the SMS / txt cache

Greetings, I need to know how to flush the cache / folder where xymon keeps its outgoing sms's.  On occasion my server will experience an issue and will over the course of an entire day send out hundreds of text messages for an issue that was resolved early in the morning. Sometimes it will send the same messages over and over again, which is what has been happening since yesterday morning.  The same 20 text messages have been sent to my phone 25 times now.
How can I purge the outstand messages that have yet to be sent?

Kenneth