Device Firmware Update (DFU)
The DFU process is done using the nRF Connect mobile app.
DFU Procedure
Start DFU firmware update mode
You can initiate DFU mode by holding the UP and DOWN buttons of the remote while it is off. Then turn it on / power on but keep pressing the UP and DOWN buttons for at least 10 seconds.Verify the bootloader starts advertising on your phone Bluetooth devices list as "TSDZ2_DFU". Now, connect to the DFU target.
Copy the DFU firmware file .zip to the phone or to the folder on PC of your choice
First download from here the firmware .ZIP file. This can be done by simply emailing the update file to your device.Use nRFConnect app to connect and do an OTA DFU using the .zip file you copied
To start the process, press the DFU button. Then click “Open Document Picker”Choose the .zip file.Click the “Start” button
The DFU will begin.the DFU process is now complete
Once the DFU process has completed, you should see that your new application (that was part of the DFU package) is now running.