Quoteit works ? if so tell me how u did it plz
Go into 'mysql' or the phpmyadmin (think that's the name, the php database management thinger).
If you have a prefix on your table name, make sure you include that too. You just need to write an update statement to get rid of all those dates:
update members set birthdate = NULL where birthdate = '2002-04-22';
If you want to make sure you are going to get the right members, you can do a select with that same Where clause first to satisfy curiosity.
Select membername,birthdate from members where birthdate = '2002-04-22';
You can use that same selecte statement after you have run the update statement to make sure you no longer have any birthdays on that date.
The drawback is if any users really do have that birthdate, you just reset it. That's a small price to pay for cleaning up all those members though.

Having the "where" clause on there is really important (if you aren't familiar with SQL), don't forget it. Without the where clause it'll reset all your member birthdates....