There is VIM's default bar below my Airline's status bar, which causes file information to be viewed twice (as shown in the image). How can I move my airline's bar to the bottom? I have tried adding set noshowmode but it didn't slove my problem.
That's not really possible.
The last line is used not only to display messages and information, but also to enter Ex commands (the commands starting with a colon, such as :w, :q, :e filename, etc.), also where you can type a search pattern if you start a search using / or ?.
Furthermore, that line is also used to display messages, such as error messages when you try to save a file but don't have permissions to write to it, or when you're searching for a term that's not present in the buffer.
The fact that the information in the message line is occasionally duplicating some information that's in the airline bar doesn't mean it should be gotten rid of.
The 'showmode' option, when set, causes Vim to display --INSERT-- in the message line when in insert mode. That's indeed a duplicated information from the one set up by the vim-airline plug-in, so the plug-in will by default disable that option to avoid that particular case of duplication.
Ctrl-Lto clear it. – B Layer Aug 17 '19 at 1:18