startcoroutine error C#

Hello, i’ve got an error in my script but I cant fix it. im new to start coroutine and IEnumerator so im sorry if it looks stupid.

Error:
`Console.TypedHelp()': not all code paths return a value

Script:

void OnGUI ()
	{
		textfieldString = GUI.TextField(new Rect(90, 450, 200, 20), textfieldString, 25);
		GUI.Label (new Rect (90, 400, 350, 100), ConsoleWindowText.ToString());
		
		if(textfieldString.Contains("/help"))
		{
			Debug.Log("Typed '/help'");
			Debug.ClearDeveloperConsole();
			StartCoroutine(TypedHelp()); // here is the error
		}
	}
//Heres the error
	IEnumerator TypedHelp ()
	{
		ConsoleWindowText = "Well Done";
	}

Had to enter a float (or other) Look at the documentary: Unity - Scripting API: MonoBehaviour.StartCoroutine

fixed script:

 void OnGUI ()
     {
         textfieldString = GUI.TextField(new Rect(90, 450, 200, 20), textfieldString, 25);
         GUI.Label (new Rect (90, 400, 350, 100), ConsoleWindowText.ToString());
         
         if(textfieldString.Contains("/help"))
         {
             Debug.Log("Typed '/help'");
             Debug.ClearDeveloperConsole();
             StartCoroutine(TypedHelp(0.5f));
         }
     }
 
     IEnumerator TypedHelp (float waitTime)
     {
         yield return new WaitForSeconds(waitTime);
         ConsoleWindowText = "Well Done";
     }