MIG files are not portable between OS versions if you use the old version to create the MIG file.
To transfer files from Windows 7 to Windows 10 you would need to use USMT 10 on the Windows 7 machine first to create the MIG andthen USMT 10 on Windows 10 to restore them.
I would grab a Windows 7 ISO and create a Windows 7 VM, then restore your files to the VM. From there you can allow VM to host communication and just transfer the files.