To open your older koala projects in the AUv3, press load in Koala and navigate to the Koala folder on your phone – there should be a songs folder in there. All your songs are in that songs folder.
If the song you want to load is a .koala file, great! You can load it straight away by tapping it – if the song is a folder, it means its a really old song, and you’ll need to open the koala app, and load and save that song to convert it to the new koala file format. Then you should be able to load it as stated above.