Why my corolla does not shift to reverse gear?

my 2001 Corolla run over a stone that cracked the Automatic transmission (overdrive type, not 3speed) oil pan which caused the car to stop changing gears since it did not have transmission oil.

Now, the AT pan was replaced and all gears are working fine EXCEPT for the Reverse gear that does not work at all, it just behaves as neutral.



How can I fix something like that? Do I have to open the transmission box? if so, what should I be looking for to justify the fact that the reverse gear does not work?Why my corolla does not shift to reverse gear?
my answer is try to check it out first on auto repair shop...Why my corolla does not shift to reverse gear?
Sorry,but reverse is gone on transmission,rebuild or replace!good luck!