Time doesn’t exist…
Correct, it is just a human tool for measurement.
Imagine it like this: We can’t go back to a previous point in time because once an event has “Happened” it can’t be Un-happened”. Once an eventy has occured, it is not “Stored” anywhere for future reference. It would be like pouring three tins of paint into a big jar and mixing them together. Once mixed you will never be able to un-mix them back into their previous forms.
BTW I know that was a bit garbled but it made sense until I had to actually write the post!