Hi Luthien,
Thanks for your message.
While the iPhone version did not include the append button, due to restricted screen size there is a capable workaround:
- Open the MIDI file
- Switch to the bar editor
- Select all bars of all tracks
- Perform a long tap to copy them
- Open the target project song, where you want to paste the copied files into
- Go to the bar editor, paste the clipboard content
Follow the Music Studio documentation link below, to learn more how to use copy and paste:
Best,
Music Studio Support