Option to select one more files to download

No problem. You install something called the file manager plug-in. It's a bit unusual for a Quickbase but it's like an add-on that is actually from Quickbase as opposed to third-party so it's free.  

If you are the main admin  for the realm, you probably have permission,  so just go to the settings for the application and you should see an option for Plug ins and follow that the installation steps. Feel free to post back if you get stuck.