Ask the person that does not believe in time travel to tell you something about themselves in relation to a historical event that happened. Ask for their name.Time travel to the past write a book about a historical event that happened in this time.Put the exact names of the people involved.Put the stuff that the person that does not believe in time travel told you in the book.Then come back to the present.
Then tell the person that does not believe in time travel the name of the book.Then to read it.
Then tell the person that does not believe in time travel the name of the book.Then to read it.