Try this
First You need to convert this string back to NSDate then again convert the NSdate to string using formatter.
NSDateFormatter *dateFormatForDB = [[NSDateFormatter alloc] init];
[dateFormatForDB setDateFormat:@"dd-MM-yyyy HH:mm a"]; //Note capital H is 4 24-hour time format
NSDate *aDate = [[[NSDate alloc] initWithTimeInterval:0 sinceDate:[dateFormatForDB dateFromString:aDateString]] autorelease];
if(aDate){
[formatter setDateFormat:@"MMM dd,yyyy"];
NSString *date = [formatter stringFromDate:aDate];
[dateFormatForDB release];
}