Need A Way To Switch Specific Data From Columns

Basically I have 635k records in a table with a person's first name, and date of birth (other stuff but it's not relavent). I imported all the data from excel files, but somehow a bunch of records got the first name and date of birth mixed up, so I'm trying to write a stored procedure that would switch the first name with the date of birth wherever the firstname is purely numeric, or something of the sort. Now records are in fact repeated so another possible but more time taking solution is to write a stored procedure that I give the date of birth and it does the switching around for the respective date of birth when it's found inside the First name. Any suggestions? All the code I've written has proved useless :/