Writing and Reading Array's to an external SD card

I am currently busy on a prototype where the Arduino can identificate people using a fingerprint sensor and shows some information about this person like name and birthdate.

The fingerprint sensor does the fingerprint matching all by itself and the only output it gives is a ID-number, for example ID = 6.

I want to use this ID number to retrieve the personal information out of an array i saved on the SD card by using the script below

#include <SPI.h>
#include <SD.h>

File myFile;

String IDnr = "0";                        // Give ID number
String Firstname = "Mike";         // Give the first name. 
String Lastname = "Mikeson";       // Give the last name 
String Birthdate = "19-07-1956";  // Give the birth date (dd-mm-yy)

String PersonalData[4] = {IDnr, Firstname, Lastname, Birthdate}; // Array met persoonsgegevens

void setup() {
  // Open serial communications and wait for port to open:
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only

  Serial.print("Initializing SD card...");

  if (!SD.begin(10)) { //CS is connected to pin 10
    Serial.println("initialization failed!");
  Serial.println("initialization done.");

  // open the file. note that only one file can be open at a time,
  // so you have to close this one before opening another.
  myFile = SD.open("IDfile.txt", FILE_WRITE);

  // if the file opened okay, write to it:
  if (myFile) {
    Serial.println("IDfile.txt succesfully opened");
    myFile.print("; ");
    myFile.print("; ");
    myFile.print("; ");

    // close the file:
  } else {
    // if the file didn't open, print an error:
    Serial.println("error opening IDalistic.txt");

void loop() {
  // nothing happens after setup

Now I can’t figure out the best way to retrieve the information using the ID number. Eventually it will store multiple entities and when I scan a finger I only want the personal information that is saved with the same ID number.

Any suggestions how I can achieve this?