Translation:That accident was declared never to have happened.
Maybe "That accident is declared as never having happened" or "that accident was declared as never having happened"
It sounds stilted to use "was declared" at all in so complex a sentence, but I might suggest "That accident was declared never to have happened."
I would have worded it similarly: "That accident was declared to have never happened."
If you think that those are correct, please report it, so that they can fix it.
The problem is you can't report problems with the English translations in the word bank, so this is the only place to point them out.
Aha...okay...what you can do is turn off the word bank and manually type your answer. If it's rejected, then you can report "My answer should be accepted".
As far as I know, the contributors/correctors only react on those reports, not on the sentence discussions.