If you would like to press specific buttons on the iOS keyboard such as DONE, DELETE and so on then you can access them by using the Accessibility Label.
This allows you to press any item on the screen (one the keyboard or elsewhere) based on its accessibility label:
The accessibility label is an internal attribute for a component that is designed to be used by screen readers etc.
You can find the accessibility label for an item by using the Accessibility Inspector on e.g. an iOS simulator. You can activate the Inspector via the General Settings.
Once you know the label, you can enter it as a parameter (exactly as it is written).
Bear in mind that accessibility labels are language-dependent and also sometime orientation dependent. It is also not necessarily the case that the accessibility label is the same as the text on the item that is visible in the AUT.