I have got it work, my solution is below:
NSMutableString *absolute=[NSMutableString stringWithString:pinPoints];
NSLog(@"before absolute: %@",absolute);
NSArray *placemarks=[absolute componentsSeparatedByString:@":"];
if([placemarks count]>5)
{
//NSLog(@"%@",[placemarks objectAtIndex:0]);
NSMutableString *string1 = [NSMutableString stringWithString: [placemarks objectAtIndex:0]];
[absolute replaceOccurrencesOfString:string1 withString:@"" options:0 range:NSMakeRange(0,[pinPoints length])];
pinPoints=absolute;
}
NSLog(@"after absolute: %@",absolute);