ScrollRect.horizontalNormalizedPosition

public float horizontalNormalizedPosition ;

Description

The horizontal scroll position as a value between 0 and 1, with 0 being at the left.

using UnityEngine;
using System.Collections;
using UnityEngine.UI;  // Required when Using UI elements.

public class ExampleClass : MonoBehaviour
{
    public ScrollRect myScrollRect;
    public Scrollbar newScrollBar;

    public void Start()
    {
        //Change the current horizontal scroll position.
        myScrollRect.horizontalNormalizedPosition = 0.5f;
    }
}