'Component.collider' is obsolete: 'Property collider has been deprecated. Use GetComponent<Collider

I keep getting this error and i't not totally sure what it is i need to change?
Assets\scripts\PlayerController.cs(72,18): error CS0619: 'Component.collider' is obsolete: 'Property collider has been deprecated. Use GetComponent<Collider>() instead. (UnityUpgradable)'

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.UI;
5. public class PlayerController : MonoBehaviour
6. {
7.     public float speed;
8.     public float JumpPower = 1f;
9.  
10.     private Vector3 moveDirection;
11.     private Rigidbody rb;
12.     private bool jump;
13.     private bool isGrounded;
14.     private Vector3 jumpDirection;
15.     private Vector3 startPos;
16.  
17.     void Start()
18.     {
19.         rb = GetComponent<Rigidbody>();
20.         startPos = rb.position;
21.  
22.     }
23.  
24.     void Update()
25.     {
26.         float moveHorizontal = Input.GetAxis("Horizontal");
27.         float moveVertical = Input.GetAxis("Vertical");
28.  
29.         jump = Input.GetButton("Jump");
30.  
31.         moveDirection = new Vector3(moveHorizontal, 0.0f, moveVertical);
32.     }
33.  
34.     void FixedUpdate()
35.     {
36.         Move();
37.         Jump();
38.     }
39.     void Move()
40.     {
41.         rb.AddForce(moveDirection * speed);
42.     }
43.     void Jump()
44.     {
45.         LayerMask layer = 1 << gameObject.layer;
46.         layer = ~layer;
47.         isGrounded = Physics.CheckSphere(transform.position, 1f, layer);
48.  
49.         if (jump && isGrounded)
50.         {
51.             rb.AddForce(jumpDirection * JumpPower, ForceMode.Impulse);
52.         }
53.     }
54.     void OnCollisionEnter(Collision collision)
55.     {
56.         jumpDirection = collision.contacts[0].normal;
57.     }
58.  
59.  
60.     void OnTriggerEnter(Collider other)
61.     {
62.         if (other.gameObject.CompareTag("Pick Up"))
63.         {
64.             other.gameObject.SetActive(false);
65.  
66.  
67.  
68.             rb.position = startPos;
69.             rb.velocity = Vector3.zero;
70.             rb.angularVelocity = Vector3.zero;
71.         }
72.         else if (collider.gameObject.CompareTag("Gameover")) ;
73.  
74.                 }
75.     }
76.  

 

Well you have it correct in line #62 but wrong in #72. Try;

Code (CSharp):

1. else if (other.gameObject.CompareTag("Gameover")) ;

 

i managed to get it working but now i have the error Gameover tag is not defined although i created a tag called Gameover and assigned it to an object