Factory resetting your Android will remove all settings—including your lock screen password—along with any contact and app information from your Android. Unfortunately, if your data isn't backed up, you won't be able to recover the information deleted by the factory reset. Every Android has its own combination of buttons which must be pressed in order to open the recovery menu; checking your Android's manual or online documentation should help you find this combination. For example, Samsung users will typically use the Power, Home, and one of the Volume buttons to access the recovery menu. Press and hold the Power button, then tap Power off when prompted. This will cause your Android to shut down. Holding down your Android's recovery keys will prompt your Android to begin booting into the recovery console. If you see a "No command" error message appear on-screen, keep holding the recovery combination for another 15 to 20 seconds. Once the recovery menu appears, use the Volume Down button to scroll down to the Recovery mode option, then press the Power button to select it.  If you don't see Recovery mode, skip this step. See the next step if you're instead met with a "No command" screen. If you're on a Pixel Android, press and hold the Power and Volume Up buttons at the same time until the recovery screen opens. Scroll down to highlight this option, then press the Power button. It's in the middle of the screen. Doing so will prompt your Android to begin factory resetting. Your Android should take under 10 minutes to completely erase. Once your Android finishes restarting, you can set it up as though it were a new phone or tablet. This will usually include selecting a language and a Wi-Fi network. When prompted, enter the email address and the password for the Google account with which you were previously signed into your Android. If you don't know the password for your Google account, use a computer to recover it before proceeding. After logging into your Google account, you can proceed with setting up the...

TL;DR in Vietnamese:
Tìm hiểu phương pháp này. Tìm tổ hợp nút "Recovery" (Khôi phục) của thiết bị Android. Tắt nguồn thiết bị Android. Ấn và giữ tổ hợp nút "Recovery". Chọn Recovery mode (Chế độ khôi phục). Bỏ qua màn hình "No command". Chọn Wipe data / factory reset (Xóa dữ liệu/Khôi phục cài đặt gốc). Chọn Yes -- delete all user data (Vâng - xóa toàn bộ dữ liệu của người dùng) ở giữa màn hình. Chờ Android hoàn tất việc xóa dữ liệu. Thiết lập Android. Đăng nhập vào tài khoản Google. Hoàn tất việc thiết lập Android.