In Music Maker Jam, you can find a list of your projects by going to the “Home” screen and then tapping on “My Music” > “Projects”.
These projects are only saved internally on the app and are not connected with your account.
This means that if you've uninstalled/reinstalled the app, deleted the app data or switched to a new device, then unfortunately there is no way to restore them.
We would recommend to back up your projects using the export option. You can then import the project whenever you require.
Please refer to the 'Project' section in the FAQ for information on how to do this.