Question How can I make touch detection for canvas objects?

Hi!
I'm making a game in Unity 2D, and on the video you can see how it works for now.
I want to make script that detects colision between arrow and circles, problem is that I made it in canvas and it's not 2D objects but UI images.
Please help me, because im begginer programmer and I can't do this.
If you have questions for this, you can ask.

Here's link do video:

Here's my ArrowController script:

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

public class ArrowController : MonoBehaviour
{

public float speed;
public bool clock;
public Text scoreText;

private int score;

void Start()
{
clock = false;
score = 0;
SetScoreText();
}
void Update()
{
if (clock == true)
{
transform.Rotate(new Vector3(0, 0, -45) * Time.deltaTime * speed);
}

if (clock == false)
{
transform.Rotate(new Vector3(0, 0, 45) * Time.deltaTime * speed);
}

if (Input.GetMouseButtonDown(0))
{
if (clock == true)
{
clock = false;
Debug.Log("Zmiana kierunku na lewy");
score = score + 1;
SetScoreText();
Debug.Log(score);

}

else
{
clock = true;
Debug.Log("Zmiana kierunku na prawy");
score = score + 1;
SetScoreText();
Debug.Log(score);
}
}

}

void SetScoreText ()
{
scoreText.text = score.ToString();
}
}

 

you can check it by the angle of the arrow, if the angle is above -45 and below 45 then you know is in the blue zone and etc for the other colors

 

Ok that good option but
Can you help me with script a little bit?

 

put a script on your arrow

Code (CSharp):

1. public class AnglesScript : MonoBehaviour{
2.  
3.  
4. void Update(){
5.  
6. Debug.Log(transform.localEulerAngles);
7. }
8.  
9. }

and see if it works to give you angles

 

Thank you buy I did it other way