On your iOS 9.3.5 device, open the App Store and go to the Purchased tab.
A custom app store accessible via Cydia that allows you to download and install older, functional app versions directly on your device. ipa+library+ios+935+free
Log in to your Apple ID on a newer device and download the app you want. On your iOS 9
These are well-known third-party libraries that provide IPA files for various iOS versions, including older tweaks and games. How to Install Apps on iOS 9.3.5 On your iOS 9.3.5 device