Rule number one of time travel, you cant change or alter the pass, what ever mistake or problem happen to you in the pass, you cant do anything about it, even if i had a machine that could now travel to the pass, i would not see the point of changing one single event in the pass that could destroy the world on the long run, remember if you could time travel i sincerely think you would not think about fixing things in the pass, you would have access to all the world knowledge and universe, what ever it is that has happen to you in the pass, learn to assimilate that event as experience and deal with it, ( not trying to be harsh here) its just life, i dont want to build a time machine to fix trivial event but to learn and explore time without damaging it .