How do you deal with negative reviews on your launch day?

Frank advice, though unpleasant to hear, is good for action.

Negative reviews on launch day sounds like: not knowing the product and people are trying to stop it. Perhaps a copy-paste message pre-cook: "Are you trying to stop a production you do not know?" Something like that could be enough.

If they are genuine ones, embrace them and work on the issues. If they are fake and hateful report them and get them taken down.