using UnityEngine;

public class Coin : MonoBehaviour
{
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        
    }

    // Update is called once per frame
    void Update()
    {
        // ★下記の１行を書いてみましょう。
        transform.Rotate(new Vector3(0, 0, 90) * Time.deltaTime);
    }
}
C#

using UnityEngine;

public class Coin : MonoBehaviour
{
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        
    }

    // Update is called once per frame
    void Update()
    {
        // ★回転速度を１０倍にする。
        transform.Rotate(new Vector3(0, 0, 90) * Time.deltaTime * 10);
    }
}
C#