Hi Declan,
You could try either “InShot” or “KineMaster” - not sure if they will run on iOS 9.3.5…
The only way to install an older version in this instance would be to use a tool like “iMazing” but you’d have to have the original app file from another device. (or jailbreaking it)
Other than that, you may be out of luck as 9.3.5 is just too old unfortunately as the newest OS version is 14.5.1.
(This is not to say the device is worthless - there are many other use cases such as digital photoframe, security camera, music player, e-book reader, etc.)
Cheers,
Chris