unflag

UNFLAG  -  remove the F indicator from the current message

Usage:  UNFLAG 

Please note that UNFLAG acts on the "current message" in your mail file,
  and not on the outgoing message.  If you are REPLYing, the current
  message is the one you are replying to.

The UNFLAG command removes the F indicator from the header line of
  the current message.  The F indicator shows that you used the FLAG 
  command to mark the message as important.  Use UNFLAG to remove 
  the FLAG.

For more help type "help" and one of these topics:
  flag   headers   message-tagging