Deleting or changing device must be done at the Administrator side. That is at selbuk.com > Login > Account managment > user ID / password > Users & Devices. On the chart of users identify the device by passing the mouse over the email-user. On the pop-up box the four digits after the date are the device ID.
Then on the chart of devices, click on the letter D belonging to the device ID.
Once the process is completed, you should go to the AppStore to install SelBuk latest version (green icon.) Keep in mind to close the AppStore and start SelBuk from the icon with the registered email-user / password. This process will register the device and the data will be downloaded from the cloud server account