How to refresh external api into db using Guzzle

I am having thismodel in my Laravel-5.8 project: Employee

Employee

class Employee extends Model { protected $table = 'employees';

   protected $primaryKey = 'id';

   protected $fillable = [
              'staff_code',
              'first_name',
              'last_name',
              'department_id',
          ];

  public function department()
  {
     return $this->belongsTo('App\Department','department_id');
  }    

}

That is,:

App\Employee

Also I have an external api that comes in form of JSON get request.

https://api.employees.net/allemployees

I have viewed it with postman get request and I have something like this:

 {
    "ID": "1",
    "StaffCode": "STC001",
    "FirstName": "Japheth",
    "LastName": "Shalom",
    "DepartmentCode": "dep2",
 },
 {
    "ID": "2",
    "StaffCode": "STC002",
   "FirstName": "Ahitophel",
   "last_name": "Nedum",
   "DepartmentCode": "dep1",
},
{
    "ID": "3",
    "StaffCode": "STC003",
    "FirstName": "Joash",
    "FirstName": "Nathan",
    "DepartmentCode": "dep2",
 },

and so on... this continues

Already I have created this function:

 use App\Employee;
 use App\Department;

 public function index() 
 {  
    $client = new GuzzleHttp\Client();
    $res = $client->request('GET','https://api.employees.net/allemployees');
    $clientdatas = json_decode($res, true);

   ...
 }

Apart from the id and staff_code that are UNIQUE, any of the others fields too can change.

Since any of the fields can change at any time. How do I refresh the entire db, save new data and update changes?

Thank you