Hi Teresa. Thanks for your question
That message comes from the “submission handler” — to know whether to display “success” or “failure” type messages. In my quick searching through the code, I believe you could leverage the tribe_events_community_submission_message filter.
However, we’ve found this Redirect to different URL after event submission plugin to solve multiple use cases (and is typically easier to implement). For example, you could redirect to a page that has your custom wording on it.
Please let me know if this workaround is satisfactory.
Have a great weekend!