How can I move my 2D main player up and down by clicking and dragging him up or down?

Add this to your object, ensuring it has a collider (which is needed to receive the mouse event);

 //
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;    
 
 public class dragMe : MonoBehaviour {
 
     private Vector3 screenPos;
     private Vector3 offset;
 
     void OnMouseDown(){
         // work out the target object is on the screen
         screenPos = Camera.main.WorldToScreenPoint (transform.position);
 
         //    store the starting position of the drag
         offset=transform.position-Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x,Input.mousePosition.y,screenPos.z));
 
     }  
 
     void OnMouseDrag(){

// convert just the Y position Vector3 currentScreenPos = new Vector3 (screenPos.x, Input.mousePosition.y, screenPos.z);

// add the resulting tranform transform.position = Camera.main.ScreenToWorldPoint (currentScreenPos) + offset;

     }
 }