Quick and dirty rotate camera around something...

CameraBehavior.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

namespace AbstractPuzzle
{
	public class CameraManager : MonoBehaviour
	{
		public GameObject cameraObject;
		public GameObject centerObject;


		/// <summary>
		/// Rotate method
		/// </summary>

		public void RotateByOffset(float offset)
		{
			cameraObject.transform.RotateAround(centerObject.transform.position, Vector3.up, offset * -0.2f);
		}

	}
}

UIInputBehavior.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;

namespace AbstractPuzzle
{
	public class UIInputBehavior : MonoBehaviour, IPointerDownHandler, IBeginDragHandler, IDragHandler, IEndDragHandler
	{
		private Vector2 lastDragPosition;
		private CameraManager cameraManager;

		/// <summary>
		/// Start
		/// </summary>

		void Start()
		{
			cameraManager = FindObjectOfType<CameraManager>();
		}

		/// <summary>
		///  IBeginDragHandler, IDragHandler, IEndDragHandler - Drag support
		/// </summary>

		public void OnBeginDrag(PointerEventData data)
		{
			//Debug.Log("OnBeginDrag()");
			lastDragPosition = data.position;
		}

		public void OnDrag(PointerEventData data)
		{
			if (lastDragPosition != null)
			{
				float offsetX = lastDragPosition.x - data.position.x;
				cameraManager.RotateByOffset(offsetX);
			}
			lastDragPosition = data.position;
		}

		public void OnEndDrag(PointerEventData data)
		{
			//Debug.Log("OnEndDrag()");
		}

	}
}