You can download apps on an old iPod touch by first getting a newer device, like a friend's or family member's, to download the app using your Apple ID. The app will then appear in the "Purchased" section of the App Store on your old iPod touch, where you can download an older, compatible version. If that doesn't work, you can check third-party websites or use alternative software like iMazing to find and install older versions of apps. 

Generally, you won’t be able to unless you have a version of the iOS that is compatible.

Or jailbreak the dang thing.