The past exists just like the present and future. It is one continuous timeline, it depends on what point you are on that timeline. In order to affect the future depends on what you do today, if you can.
You can use info from yesterday to ascertain today and plan for tomorrow, albeit with unknown variables. So it all exists simultaneously. The point of observer just differs.
If the past EXIST (it doesn't but you claim it does)
why is it nobody goes there for a visit? or go to the future to see what you will be doing?
Only NOW exist and NOW is the only moment any observer is capable of experiencing