Restore old app from previous itunes Backup

Hey all - I have my iPhone 8+ that updated an app that is horrible compared to the previous version. I have the previous version on an iTunes backup on my Mac El Capitan 10.11.6 but apparently iTunes cannot restore a single application anymore. I have iTunes 12.7 on Mac and IOS 12.1 on my iPhone.
Any help or hope with retrieving the previous version?
However, that may be the only way to restore just THAT app.
Another thought, although again, I haven't tried it, is to use an app like 'unpkg' to extract that one app from your iTunes backup. Worth a try.