Do you use an older version of this iPrint app on your iPad now?
Does the older version still work on your iPad?
Find another printer app that still supports iOS 9.3.5.
This does not make your iPad useless and obsolete.
This WILL happen more and more as time progresses and as app developers move on to supporting newer iOS versions.
This will be inevitable.
So, far that iPad has lasted over 2-1/2 years more since Apple stopped supporting it under iOS 9.3.5.
Older iPads are 6 and 7 years old, now and are underpowered for both a newer iOS and apps that support newer iOS versions.
Until all app support for older iOS and 32-bit iDevices completely ends, older devices will still be useful for a little while longer.
Tap on both of my links below.
iOS 10/11 and iPad 2, 3 & 1st generation iPad Mini Compatibility
Many newer iOS 10 app updates may still have older versions to download from the iOS App Store.
Downloading Older iOS 9.3.5 Versions of Apps ONLY Available Now for iOS 10 or Later
Good Luck to You!