Hey there! Hello!
I'm certainly not an expert at anything related to ethernet, but I do believe that the answer you're looking for is a jam signal. To my limited understanding, CSMA/CD makes computers "listen" before sending data to see if their signal is currently being used. If it's not, it'll send. The computer and sender will continue to "listen" to see if a jam still occurred afterwards. If one did occur, a jam signal will be sent to everyone who may send something over that signal, warning them not to send anything else, since it will not be successful and may make the jam worse.
Hope this helped you out! I would normally tell the question–askers that they can ask me any additional questions they may have, but... that's the extent that I know about ethernet, haha! :-)