Due to Apple removing support for 3D Touch on the iPhone XR, cursor control no longer works on Microsoft SwiftKey Keyboard.
If your device supports 3D Touch it is possible to trigger cursor control by pressing down firmly in the keyboard area.
On iPhones without 3D Touch, cursor control can be triggered by long pressing the spacebar.
For both methods, you can then move your finger to reposition the cursor.
Note: On Microsoft SwiftKey we use the spacebar to switch between different languages and layouts. Therefore, if using the spacebar, it is not possible to invoke cursor control if more than one layout is selected in your Language settings.