Cant Get Dialogue Trigger Working

I know it's been asked a lot but I cant find a solution anywhere. Im trying to create a basic dialogue system where the end goal is that I can approach an NPC and start dialogue after either clicking on it or pressing a button. I have the dialogue part and it works fine, but I cant figure out a trigger. Here's my code for the dialogue.

using System.Collections; using System.Collections.Generic; using UnityEngine; using TMPro;

public class Dialogue : MonoBehaviour{

 public TextMeshProUGUI textDisplay;
 public string[] sentences; // holds all sentences
 private int index; //int variable
 public float typingSpeed; 
 public string name;
 public GameObject continueButton;
 public Animator animator;


 void update (){

     if(textDisplay.text == sentences[index]){
         continueButton.SetActive(true);
     }
 }


  // Start is called before the first frame update
 public void StartDialogue(){
      animator.SetBool("IsOpen", true);
    
      StartCoroutine(Type());
 }
 
 public IEnumerator Type(){ //coroutine

     foreach(char letter in sentences[index].ToCharArray()){
         textDisplay.text += letter;
         yield return new WaitForSeconds(typingSpeed);
         //delays code by typing speed
     }
 } 

 public void NextSentence(){


     if (index < sentences.Length - 1){ //if we are at the end of dialogue
         index++; //increments the characters
         textDisplay.text = "";
         StartCoroutine(Type());
     } else {
         textDisplay.text = "";
         continueButton.SetActive(false); //disables cont at end of dialogue
         animator.SetBool("IsOpen", false);
     }
 }

}