Use at you own risk
download and unzip thunderboard-default.zip and drag the thunderboard-default.s37 file to your Thunderboard2 pop up folder to reset the board.
When I first tried the ThunderBoard2 I was very imprerssed with the out-of-the-box Android (and IOS) BLE phone connection to the board. Very fancy to get up and running immediately. I then tried installing a few of my recent ei- libraries, see above files and then I was shocked that I could not reset the board. After a few days of installing software and about 7 Gb later almost breaking my old desktop (I was also installing the full NRF-Connect) I found out that in the demos are compiled as a temp file and installed directly to the thunderboard. This default app is called (Bluetooth-SoC-Thunderboard Sense 2), but they don't actually give you the file. (Probably some reason for that) and when you dig for it, it has the special format .s37. This is a bit of a waste of the amazing pop-up folder that allows drag and drop installation of files.
So I tried a blinky program to make sure my board was working, then dragged the .s37 file to the popup thunderboard folder it reset the thunderboard back to factory setting that work with the app!
I then tried putting the .s37 file on this github and you can download .bin files but not .s37 files. I then zipped it and you can download that. I then changed the file name from .s37 to .bin and it still installs changing blinky back to the default app. Unfortuanately this .bin file is also not allowed to direct download from github and it shows exactly like the .s37 file so I deleted it. Not sure why SiliconLabs does not give this .bin file out (Probably a reason) as I was very upset when I thought I had basically bricked my board. The installation of the Silicon labs Simplicity setup is a large install and completely filled up almost making my old desktop un-useable (On second thought I think NRF-connect is the large installtion, oh well).
I hope this bin is helpful to others who also have that sense of panick that you have bricked a new board.
download and unzip thunderboard-default.zip and drag the thunderboard-default.s37 file to your Thunderboard2 pop up folder to reset the board.
https://www.silabs.com/development-tools/thunderboard/thunderboard-sense-two-kit
https://account.mbed.com/login
Useful locations when using Simplicity Studio
https://www.silabs.com/developers/simplicity-studio
C:\Users\USERNAME\AppData\Local\Arduino15\packages\arduino\hardware\mbed\1.3.2
C:\SiliconLabs\SimplicityStudio\v5\developer\sdks\gecko_sdk_suite\v3.1\app\bluetooth\demos