Open Retail stores, choose a store and go to Terminals. The AfroPin Terminal for Android card has a download button, a link you can copy and a QR code. On the POS device, open the link or scan the QR code, download the app and install it.
Android may ask you to allow installs from your browser the first time. The app works on Android 6 and later, for brand and reseller tills alike: it shows each till the tasks its account can do.