I'm building a time machine and need help!?

Hello I'm seriouslly building a time machine and need help doing it, does anyone have any advice or experiance doing it? I have to go back in time about at least 5 months and fix something that happened. Any help or advice would be very welcomed! Thank You
Update: Ok heres another question for you why are you people not taking me seriouslly?
Update 2: "You can't change the past. The only way to "fix" it is to apologize and do damage control. Remember in the future to never do something that you would have undone"

Ok why can't you change the past? Serious question why can't you change it?
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