Professional advice from a computer professional.
Check to see if anybody has already responded informing the sender of the mistake.
If so DO NOTHING. It will end eventually.
If not, reply ONLY to the sender informing them of the error. Ask them to reply to the original email, explain the mistake, and move everyone to the BCC list on the reply.
This way hopefully the impending flood of future replies will only go to the original sender.
Now wait it out. It will end eventually.
Under no circumstances should you ever:
Reply All to tell the sender about the mistake.
Reply All to request no more replies when eleven other people have already done so.
Reply All to tell people to stop replying all.
Reply All to tell the person who replied all to stop people from replying all that they’re not helping.
Reply All and say “ugh he said stop you’re just making it worse.”
Reply All and say “this is annoying”.
Reply All and say “Can you remove me from this email?”
Reply All and say “I’m not sure what this conversation is about. Can someone clarify what is expected of me?”
Reply All to the above people explaining what is going on.
Reply All to complain about poor handling of Reply All.
Reply All with a joke about how bad noobs are at email.
Basically just don’t Reply All.
And remember the BCC trick.