No, you don’t “know” that.

Unless you are God or equal with God, and if so, God has not disclosed this wonderful news to us yet.
And I will add that even God does not close the door. His mercy,
and our ability to change, continues until our death.
His mercy makes possible our perpetual opportunity to change.
History, including very contemporary history, is filled with examples of people who believed they “couldn’t change,” and/or were “believed” (by others) or “known” (by supposedly omniscient other perons) to be “unable to change” or “definitely couldn’t” change.