Anyone (not just you as the website admin) can use the small "Feedback" link just below the info box to dispute any of the pieces, but I'm not sure if a single report will even be seen by a human.
Depending on your role/responsibilities with the company, you can verify yourself as an authorized representative and/or submit a legal removal report.
However, all three methods I just mentioned are considered by Google as "suggested changes" and it will continue to publish whatever the machine thinks of your event, basically.
Recent example: Search for "UFC 257 canceled" and read about it.
This same thing happened with UFC 257 earlier in the month. Just days before the event, Google showed it was canceled with the same red text in the info box (knowledge panel). Google continued to show it as canceled during and after the event. When searching "UFC 257" on Google you would see results and news snippets covering the event while at the same time Google claimed the event never happened.
It was almost a week after the event that Google removed the text, despite thousands of people talking about it online and the massive worldwide popularity of the UFC. I can only assume that smaller events without as much online chatter would have much less chance of changing Google's mind. Google probably covers itself in bulletproof terms and conditions, so it was in no hurry even though the misleading information definitely caused public confusion and financial damage to the UFC.