Hello Paul F.
I loged in to App center as you suggested and found the list of the Apps. The only icon next to them is the delete icon. Try to find a way around it but no luck. At the begining of the Intel App Center page it says you can find your files once you logged in into Intel XDK, but even there it is not accesible. I would appriciate any extra guidance.
Unfortunately i couldn't find the APK files i had.
P.S : Diego thank you for the lead to Paul's post.
Are they published apps?
If so try downloading the APK files from the Google Play Store using something like "DirectAPK Downloader" (It's a Google Chrome extension)
Once you have the APK files, rename them to ZIP files and your www folder should be inside the ZIP file.
Yonas -- that is a recent change to App Center that you are seeing. If you go to the Build tab in the XDK you can download the last successful build (if it was in the last 30 days) from the build tiles. If that does not work, you can make a request by sending an email with this email form (https://appcenter.html5tools-software.intel.com/xdkissue/) and we might be able to retrieve a source bundle from your account. You need to use the email address for the same email account that you use to log into the XDK in order to insure authenticity of the request and receive replies.