To delete a reminder entered with the REMIND command, simply type
CANCEL<return> to the monitor.  Your pending reminders will be
listed and you can selectively delete them.  If you answer the
deletion question with the letter L (for List), the remaining
reminders will be listed without allowing deletion.

For more information, see the MAIL section and the MAIL appendix in the
Monitor Command Manual, SAILON-54.6, online as MONCOM.BH[S,DOC].