Bạn cần chắc rằng video mà bạn muốn lưu được gửi đi từ Camera Roll. Mở Messenger. Truy cập video. Nhấn giữ lâu trên video. Nhấn vào Save (Lưu) trong thanh công cụ cuối màn hình.

Given the above summary, write a detailed text in English for it.
If the video in question was shared from Facebook, you can't use this section to save the video. However, if you or a friend uploaded the video to the conversation from a phone, tablet, or computer, you should be able to save it from the conversation onto your Camera Roll. Tap the Messenger app icon, which resembles a white speech bubble with a blue lightning bolt in it, on the phone or table onto which you want to save your video. If you aren't logged into Messenger, enter your login information when prompted before proceeding. Select the conversation to which the video was sent, then scroll to the video. Doing so will cause a few different options to appear, one of which is a toolbar at the bottom of the screen. It's in the toolbar at the bottom of the screen. Doing so will prompt the video to save onto your Camera Roll, though it may take a few minutes for the video to appear there.  On Android, you'll tap Save Video here. If the video doesn't download after a couple of minutes, re-open Messenger and try again, making sure to leave Messenger open until the video downloads.