You can find this on the far right side of the upper menu. Press Up on the main PS4 menu to open the upper menu. You don't need to sign in with your PlayStation Network account to access your PS4. It should appear on the Connect to PS4 screen, with the words "Powered On" underneath. If your PlayStation is not appearing, double-check both systems to ensure that they are connected to the same network. Tap the Refresh button to scan again. This code will authorize your device to connect to the PS4. The number will be eight digits.

TL;DR in Vietnamese:
Mở thực đơn Settings trên PS4. Mở ứng dụng PlayStation trên thiết bị di động. Nhấn vào máy PS4 của bạn. Nhập mã mà PS4 đã hiển thị.