unity – WaitForSeconds Error – Game Development Stack Exchange

I'm new to c # and coding, sorry if I look like a noob … I do not know how to fix waitforseconds error, and I do not know what's wrong.

float public restartDelay = 2f;

textMesh public failText;
TextMesh public failTextGame;

private void Start ()
{
failTextGame.text = "";
}

System.Collections.Generic.IEnumerable OnTriggerEnter (Collider other)

{
if (other.gameObject.CompareTag ("Wall"))

{

failText.text = "The game is over!";
failTextGame.text = "Retry";
return return new WaitForSeconds (restartDelay);
SceneManager.LoadScene (SceneManager.GetActiveScene (). Name);
}
}

}