Getting Bad Request

Bad Request
Your browser sent a request that this server could not understand.
Request header field is missing ‘:’ separator.

Getting the above message when loading my site. Any help would be appreciated.

Issue: I had accidentally set a corrupted value in browser cookies. Later I found that cookie and removed from being set. So, this error won’t happen for new users. But for already loaded users, have this cookie stored in their browsers. Hence, without clearing cookie those visitors will face loading error.

I would like to know how to set that cookie from the server itself(through response header) when it is failing like above.

Please help me out on this.