Please follow steps below:

1. Download "nRF Toolbox".

AppStore: https://apps.apple.com/us/app/nrf-toolbox/id820906058

GooglePlay: https://play.google.com/store/apps/details?id=no.nordicsemi.android.nrftoolbox&hl=en_US

2. Tap the file "app_dfu_v9.zip".

This is file attached to the email.

3. Share this file with nRF Toolbox. To do this:

3.1 Tap "Share" icon in the top right corner (looks like a box wirh an arrow pointing up).

3.2. Choose "Copy to nRF Toolbox". If you don't see "nRF Toolbox" please swipe left and tap "More" (looks like three dots). 

3.3. Find "Copy to nRF Toolbox". 

3.4. The "nRF Toolbox" will be open automatically. Please check that name of the fileis "app_dfu_v9.zip". 

4. Press the SOS button on the device and DON'T release it. 

5. With pressed SOS button put the device on the charger for a few seconds.

6. Remove device from charger and release the SOS button. 

7. The blue light will appear. It means that the device is ready for uploading a new firmware. 

8. Tap "Select device" in "nRF Toolbox".

9. Find device.

Please check that name of the device is appear on the top.

10. Tap "Upload".

11. Wait till 100%.