TypeWriter effect on existing dialogue system?

I watched a video series on youtube on how to make a dialogue system for my game, this is the link " https://www.youtube.com/watch?v=BrCxFpZFRS0&t=787s ". the video has 3 parts and i watched all 3 but it does not explain how to make a typewriter effect (I thought it did). can any one help me and explain how to add that effect?

 public class DialogueManager : MonoBehaviour
 {
     public GameObject dBox;
     public Text dText;
 
     public bool dialogActive;
 
     [TextArea(3, 10)]
     public string[] dialogLines;
     public int currentLine;
 
     private PlayerMovement thePlayer;
 
     // Start is called before the first frame update
     void Start()
     {
         thePlayer = FindObjectOfType<PlayerMovement>();
     }
 
     // Update is called once per frame
     void Update()
     {
         if (dialogActive && Input.GetKeyDown(KeyCode.Q))
         {
             //dBox.SetActive(false);
             //dialogActive = false;
 
             currentLine++;
         }
 
         if(currentLine >= dialogLines.Length)
         {
             dBox.SetActive(false);
             dialogActive = false;
 
             currentLine = 0;
             thePlayer.canMove = true;
             GameObject.Find("Player").GetComponent<PlayerMovement>().enabled = true;
         }
 
         dText.text = dialogLines[currentLine];
     }
 
     public void ShowBox(string dialogue)
     {
         dialogActive = true;
         dBox.SetActive(true);
         dText.text = dialogue;
     }
 
     public void ShowDialogue()
     {
         dialogActive = true;
         dBox.SetActive(true);
         thePlayer.canMove = false;
         GameObject.Find("Player").GetComponent<PlayerMovement>().enabled = false;
     }
 }



  public class dialogHolder : MonoBehaviour
 {
     public string dialogue;
     private DialogueManager dMAn;
 
     [TextArea(3, 10)]
     public string[] dialogueLines;
 
     // Start is called before the first frame update
     void Start()
     {
         dMAn = FindObjectOfType<DialogueManager>();
     }
 
     // Update is called once per frame
     void Update()
     {
         
     }
 
     void OnTriggerStay2D(Collider2D other)
     {
         if(other.gameObject.tag == "Player")
         {
             if(Input.GetKeyUp(KeyCode.E))
             {
                 //dMAn.ShowBox(dialogue);
 
                 if (!dMAn.dialogActive)
                 {
                     SoundManagerScript.PlaySound("talk");
                     dMAn.dialogLines = dialogueLines;
                     dMAn.currentLine = 0;
                     dMAn.ShowDialogue();
                 }
             }
         }
     }
 }