Unless I’m mistaken, those are the screen navigation buttons, with the triangle rotating when the keyboard is open, and tappable to close the keyboard. To change the layout, you’d have to mirror the two outer buttons in Settings, Home Screen, or wherever it would be on that phone.
The option to use gestures instead of buttons is probably also there.
The OP's issue is that when the keyboard is showing, the Back arrow turns into an arrow pointing down (meaning that tapping it makes the keyboard go down, i.e. go away).
Adding a virtual Back button may help, since that may have only the back function, rather than the hide-keyboard function. Look in the Play Store for suitable apps.