It's a dark-blue app with a white "f" on it. Doing so will open your News Feed if you're logged into Facebook. If you aren't logged in, first enter your email address (or phone number) and password. It's either in the bottom-right corner of the screen (iPhone) or in the top-right corner of the screen (Android). You'll find this option toward the bottom of the menu. Skip this step for Android. It's either at the top of a pop-up menu (iPhone) or toward the bottom of the ☰ menu (Android). This option is near the bottom of the screen and has a red caution circle next to it. On this page, you'll see a list of people who you've blocked in the past; you can choose to unblock any of them. It's a blue button on the left side of the page. Doing so will unblock your selected user. If you want to re-block the user, you'll have to wait for 48 hours before you can block them again.

How would you rephrase that briefly using Vietnamese?
Mở Facebook. Chạm vào ☰. Kéo xuống và chọn Settings (Cài đặt) ở bên dưới trình đơn. Chọn Account Settings (Cài đặt tài khoản). Chọn Blocking (Chặn) ở gần bên dưới màn hình với biểu tượng cảnh báo màu đỏ ở bên cạnh. Chạm vào Unblock (Bỏ chặn) ở bên phải tên người dùng. Chọn Unblock (Bỏ chặn) khi được hỏi.