We Can't Pray for Something in the Past

Prayer affects but does not change what happened. Even though you might not care to pray for something where you know the outcome as long as you're not contradicting the outcome you're not doing anything fundamentally wrong. For example we know that on 9-11 some people died when the Twin Towers collapsed and I think it would be foolish to pray that in our timeline You could always pray for other timelines to think this. All of this is consistent with having a single timeline where God affects the different portions of the timeline based on our prayers, although multiverse could exist.