How to add multiple files to opencart at once?

Question

opencart

Good afternoon!
Faced such a problem, there is a feedback form on the site, in which there is a button to upload a file. When selecting several files, an example of txt files, it sends the last selected one in the letter, that is, if you select 1.txt and 2.txt, then 2.txt comes in the letter
. upload and it uploads this last file to the directory and sends
it. I don’t understand much how you can change this controller to send several files at once
Opencart version 2.1.1