We realized that installing extensions in newer Chrome had been changed. There was an Extensions Windows to let user search extensions, select an extension and install selected extension before, but now we can not see the same Extensions Window.
The Extensions Window is actually still there, but we can not search extensions and install extensions, we can only see installed extensions from there. Because Google changed Chrome Extensions management. If we want to install extensions, we should use Chrome Web Store.
You can either click Chrome Web Store link directly, or use the following steps to open Chrome Web Store:
Three dots on the top right corner of Chrome, then select More tools, then Extensions:
In Extensions Window, select 3 short lines (Settings) icon on the top left corner to open Setting panel, then select Open Chrome Web Store on the very bottom of the panel.
Now you see the Chrome Web Store window, from the window, you can search an extension in the search box (top left corner) and install it.