To disconnect your current reader from your iOS device, first click the drop down menu within the app. Then, click 'My Devices'
Once your device screen has appeared, click 'change device'. An alert should appear with the following text: "are you sure you want to change device as this will disconnect the current one". Click 'OK'
This will take you to your settings. Click on the arrow by 'Bluetooth' to get to the Bluetooth menu.
A list of your devices will appear. Click on the info icon. You will then be prompted to either 'Disconnect' or 'Forget This Device'. Click 'Forget This Device'.