How to find the index of the clicked UI button?

Hi,
I want help with picking and adding materials to the Object dynamically

Here is my process:

Will click on a GameObject, The variants of the gameObject will appear in a UI called Customize. The UI will have Variant buttons and clicking on a particular Variant button, the material associated with that variant has to be applied to GameObject. The GameObject will have a script and here is what I'll define the variants:
and here is how the UI is

Can someone please help me with finding the associated variant materials on click and adding them to the game object?
It is also great if i can just know the index of element and variant

here is the code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class CSV_ObjectCustomizer1 : MonoBehaviour {
 
     public List<ProductsYo> Elements = new List<ProductsYo> ();
     private GameObject MainCanvas = null;
     private GameObject CSVItems = null;
 
     void OnMouseDown(){
         if (Input.GetMouseButtonDown (0)) {
             OnPupulate ();
         }
     }
 
     void OnPupulate(){
         MainCanvas = GameObject.Find ("CSV_Content");
         if (MainCanvas.transform.childCount>0) {
             ClearChildren ();
         }
         for (int i = 0; i < Elements.Count; i++) {
             GameObject CSV_ItemPanel = Instantiate(Resources.Load ("CSV_ItemPanel") as GameObject);
             if (CSV_ItemPanel.GetComponentInChildren<Text> ().transform.name == "ItemName") {
                 CSV_ItemPanel.GetComponentInChildren<Text> ().text = Elements [i].ItemName;
             }
             CSV_ItemPanel.transform.SetParent (MainCanvas.transform, false);
 
 
             for (int j = 0; j < Elements [i].Variants.Count; j++) {
                 Debug.Log (Elements[i].ItemName+ Elements [i].Variants [j].VariantName);
                 GameObject CSV_ItemButton = Instantiate (Resources.Load ("CSV_ItemButton") as GameObject);
                 CSV_ItemButton.transform.Find("CSV_VariantName").gameObject.GetComponent<Text>().text = Elements[i].Variants[j].VariantName;
                 CSV_ItemButton.transform.Find ("CSV_VariantIcon").gameObject.GetComponent<Image> ().sprite = Elements [i].Variants [j].VariantIcon;
                 CSV_ItemButton.transform.SetParent (CSV_ItemPanel.transform.Find("CSV_Items"), false);
 
                 //Here is what i'm stuck:
                 CSV_ItemButton.GetComponent<Button> ().onClick.AddListener (() => OnVariantButtonClicked(i,j));
             }
         }
 
 
     }
 
     void ClearChildren(){
         MainCanvas = GameObject.Find ("CSV_Content");
         Transform[] Children = MainCanvas.GetComponentsInChildren<RectTransform> ();
         while (MainCanvas.transform.childCount > 0)
         {
             Transform child = MainCanvas.transform.GetChild(0);
             Destroy(child.gameObject);
         }
     }
 
     //Here is what i'm stuck
     void OnVariantButtonClicked(int ElementIndex, int VariantIndex){
         Debug.Log (ElementIndex + "," + VariantIndex);
 
     }
 }
 

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using System;
 
 
 [Serializable]
 public struct ElementInfo{
     public string VariantName;
     public Sprite VariantIcon;
     public Material VariantMaterial;
 
 }
 
 [Serializable]
 public class ProductsYo{
     public string ItemName;
     public List<ElementInfo> Variants = new List<ElementInfo>();
 }