This tutorial will guide you on saving a video from a WeChat conversation to your computer.
Follow These Steps

Launch WeChat on your PC. You can save videos using either the Windows or macOS WeChat applications, or even the WeChat web browser app.

Sign in to WeChat. If you're not already logged in, make sure to have your phone or tablet nearby to log in now.

Select the chat containing the video. Your chats are displayed on the left side of the screen. If you can't see them, click the chat bubble icon near the top-left corner of WeChat first.

Right-click on the video. If your computer lacks a right mouse button, hold down the Control key as you click with the left button to bring up a pop-up menu.

Click Save As…. This action will open your computer's file browser.

Double-click on the folder where you wish to save the file.

Click Save. The video will begin downloading to your computer. The download time varies depending on its size, ranging from a few seconds to several minutes.