[Help] Add Click + Drag functionality to my camera

I’ve been trying to make a third-person camera with zooming functionality that I can control manually via right-clicking and dragging; however, when I attempt to add said functionality, the camera is disabled due to me being unsure where I have to put my if statement of inputting the right mouse button. I’m using the Unity 2021 editor if that information helps people figure out my situation.

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

public class CameraController : MonoBehaviour
    private const float LOW_LIMIT = 0.0f;
    private const float HIGH_LIMIT = 85.0f;

    private float _mouseSensitivity = 3.0f;

    private float _rotationY;
    private float _rotationX;

    private Transform _target;

    private float _distanceFromTarget = 3.0f;
    private float ScrollSpeed = 40;

    private Vector3 _currentRotation;
    private Vector3 _smoothvelocity = Vector3.zero;

    private float _smoothTime = 0.2f;

    private Vector2 _rotationXMinMax = new Vector2(-40, 40);

    void Update()
            float mouseX = Input.GetAxis("Mouse X") * _mouseSensitivity;
            float mouseY = Input.GetAxis("Mouse Y") * _mouseSensitivity;

            _rotationY += mouseX;
            _rotationX += mouseY;

            _rotationX = Mathf.Clamp(_rotationX, _rotationXMinMax.x, _rotationXMinMax.y);

            Vector3 nextRotation = new Vector3(_rotationX, _rotationY);

            _currentRotation = Vector3.SmoothDamp(_currentRotation, nextRotation, ref _smoothvelocity, _smoothTime);
            transform.localEulerAngles = _currentRotation;

            transform.position = _target.position - transform.forward * _distanceFromTarget;

            _distanceFromTarget -= Input.GetAxis("Mouse ScrollWheel") * ScrollSpeed;