You can't reverse the priority and make it right to left. What you can do is request a range of dates off (select the 1st through the 8th) and then select the reverse order but that actually places them on your bid starting with the 8th and working left to right down to the first.

I think that it is easier to just request the dates off that you want in the order you want them and the order you want them removed from your bid (if it gets to that line in denial mode).