can not access variable of prefab script

I have a script "conversation" to instantiate a prefab and a method "ImportTextFile" with an array as a return type and with a hard reference to a prefab "DialoguePrefab" . Before the prefab is instantiated I want to approach the prefab script "Dialogue" to set the variable "public DialogueStrings" equal to the returntype of my method from the "conversation" script. i thought "DialoguePrefab.GetComponent().DialogueStrings = ImportTextFile("testB");" would do the trick but I get the following error: Object reference not set to an instance of an object.. What am I doing wrong?

 public class conversation : MonoBehaviour
 {
     public GameObject DialoguePrefab;
     public Transform DialogueHolder;
     public float DialogueOffsetX = 5f;
     public float DialogueOffsetY = -0.75f;
 
     private GameObject DialoguePrefabClone;
     private GameObject canvas;
     private bool isHit;
 
     void Start()
     {
         isHit = false;
         canvas = GameObject.Find("Canvas");
 
         //DialoguePrefab.GetComponent<Dialogue>().DialogueStrings = ImportTextFile("testB");
     }
 
     void OnTriggerEnter(Collider other)
     {
         if (other.name == "Player" && !isHit)
         {
             DialoguePrefabClone = Instantiate(DialoguePrefab);
             Vector2 screenPosition = Camera.main.WorldToScreenPoint(new Vector2(DialogueHolder.position.x + DialogueOffsetX, DialogueHolder.position.y + DialogueOffsetY));
             DialoguePrefabClone.transform.SetParent(canvas.transform, false);
             DialoguePrefabClone.transform.position = screenPosition;
             isHit = true;
         }
     }
 
     public string[] ImportTextFile(string textFile)
     {
         string[] DialogueStrings = new string[10];
         TextAsset TextFileToLoad = (TextAsset)Resources.Load(textFile);
         if (TextFileToLoad != null)
         {
             DialogueStrings = new string[1];
             DialogueStrings = (TextFileToLoad.text.Split('\n'));
         }
         return DialogueStrings;
     }
 }