Hi @price1h, and welcome to the forum! In the lesson “songs for module 2”, it says:
" Here are some songs in the APP that I recommend you check out. …
- Leaving on a Jet Plane - John Denver"
Now, I don’t have the lessons & songs app anymore, so I can’t check, but I’m guessing that in the app, the chords GCD have been transposed to ADE (G->A, C->D, D->E). This way, the song in the app will sound a whole note higher than the original, but it will indeed allow you to play it with ADE. The app is mostly targeted at beginners, and as such, quite a few of the songs in the app are simplified version or have been transposed to avoid the more difficult chords or to allow you to play them even at a beginner level.
If you don’t have the app, I would rather advise you to stick to one of the other songs listed for which the original has indeed the chords A, D and E.
Hope this helps!