1. Start Magic Dosbox
2. Tap the orange “+” icon on the left
3. Tap “Import profile” (the box icon)
4. Browse to the location of your .mgc file (if you downloaded it to your phone, most likely in /sdcard/Download)
5. That’s it.

Mind that you’ll have to adjust the mountings, because the .mgc files will point to the folders where the person uploading the file stored his/her game, and this will most likely differ from your folder structure.