Before capture, move the focus rectangle to the spot that should be sharp in the final image. For a visualization of the depth map, tap the box symbol button on the capture screen.
More information can be found on our blog: https://www.procamera-app.com/en/blog/whats-new-in-procamera-v13-4-portrait-mode-update/
After you have taken your shot, you can change which area is sharp by moving the focus rectangle around, and adjust the intensity of the depth blur:
Open your photo, tap Edit. Then select depth editing tools by tapping the box icon or the face icon far left. Tap to set the focus rectangle (or drag it around) and swipe up and down anywhere on the screen to change the intensity of the simulated aperture (depth blur).
More detail in our blog post: https://www.procamera-app.com/en/blog/whats-new-in-procamera-v12-0-portrait-mode-album-selector-filters/