If you have multiple XML files to upload to AppColl, you can combine them all into a zip file and then import the single zip file into AppColl using the big blue arrow at the top of the page. Be sure to create the zip file without any subfolders, as AppColl will ignore any files in subfolders.
When importing zip files, AppColl will process the XML files using a background task. As the files import, the number of files remaining to be processed will be displayed in the big blue arrow.