The touchscreen interface of modern smart phones and tablets is probably the easiest and most intuitive interface to a computing device that has ever been invented. However if you have a physical disability that prohibits you from operating a touchscreen, a world of useful applications that is at the fingertips of most people may be impossible for you to use.
All is not lost because of a special feature built into the iOS operating system that allows you almost complete access to all of the device's capabilities via a feature called "switch control". If you can operate at least one switch, it can be connected to a Bluetooth Low Energy (BLE) device and you can scan through rows and columns of icons and select the application you want to run. Once inside the app you can tap anywhere on the screen, scan through options to be selected, or type a message. The YouTube video below demonstrates how switch control works. This video was created on an iPad Mini 2 using the techniques described in this tutorial. It will work on any device running iOS 9 or greater.
Complete details on how to use switch control accessibility from iOS can be found on the Apple website at https://support.apple.com/en-us/HT201370
There are some additional tutorial videos and other resources on the last page of this tutorial under "Final Thoughts" that may be of interest to you.
Commercially made Bluetooth switches can be purchased from a variety of companies who specialize in assistive technology but the prices can run from $180 up to $500 or more. We can use our maker skills, the power of Arduino compatible processors, and a few parts from the Adafruit store and build our own custom device for a fraction of that cost. Not only can a maker-built device save considerable money, if you have access to a 3D printer, laser cutter, or CNC devices you can create a device especially suited to the particular needs of the user. You have the flexibility that may not be available from a commercially built device.
Check this reference webpage link or the specifications for your model to verify BLE compatibility.