It really depends both on how you mean I know it, and what the answer is.
Unless the source is really believable somehow, I’m not likely to believe it.
If I do believe it, and it’s some fairly distant time, then I’m liable to be really annoyed to learn that the universe works that way, and act out my upset somehow to demonstrate my dissatisfaction. However I’ve seen enough cautionary tales to realize that just because I can’t die in other ways, doesn’t mean the tormenting powers-that-be won’t give me some worse-than-death torment instead. So I’d probably just try to spoil their parade by ranting about how the universe is annoying setup with predetermination so why care or bother, and share my information about my exact future time/death.
And then I might decide to just meditate into oblivion instead of caring about trying to affect any material outcome.