How Can I make a platform swing left and right

so far this is what i have.

using UnityEngine;
using System.Collections;

public class swingPlatform : MonoBehaviour
{
public int left = 0;
public int right = 0;
public int speed = 60;

void Update() 
{
    gameObject.transform.Rotate(0, 0, speed * Time.deltaTime);
	
	
	 if(gameObject.transform.rotation.z > left)
	{
		 gameObject.transform.Rotate(0, 0, speed * Time.deltaTime);
	}
		else if (gameObject.transform.rotation.z < right)
		{
   			 gameObject.transform.Rotate(0, 0, -speed * Time.deltaTime);
		}
	}

}

Here is a bit of code that rotates the platform back and forth. The code produces an eased movement at the ends of the rotation. For a non-eased movement, switch to the line commented out:

using UnityEngine;
using System.Collections;
 
public class Flipper : MonoBehaviour {
	public float speed = 1.0f;
	public float maxRotation = 30.0f;
	
	void Update() {
	transform.rotation = Quaternion.Euler(0.0f, 0.0f, maxRotation * Mathf.Sin(Time.time * speed));
	//transform.rotation = Quaternion.Euler(0.0f, 0.0f, maxRotation * (Mathf.PingPong(Time.time * speed, 2.0f)-1.0f));
	}
}