How to reset a custom pivot table row label

I frequently rename pivot table rows. For example in a row using a STATE column, I might rename values as follows: TX = Texas, CA = California, etc. Recently I had a pivot table using a DATE column and someone accidently renamed a date as text and the DATE column no longer sorts properly. How do I reset to default and tell the Pivot Table to undo any renamed row label values using the raw data as the row labels again?