This is a firmware to be used to flash ESP8266 chip.
The firmware contains an adapted and bit re-coded version of original HomeBrew 2.0 and Pegaswitch hack for Switch that you can also find here: https://github.com/switchbrew/nx-hbexploit300
You can use next program to flash ESP8266 chip. This application is available for Windows x86, Windows x86_64, y MacOSX.
https://github.com/marcelstoer/nodemcu-pyflasher/releases/tag/v3.0
1.- Download firmware from this repository.
2.- Download and Run the pyflasher Application you can download from the link above.
3.- Select the firmware.
4.- Select the COM port.
5.- Program the flash memory of the ESP8266 chip.
6.- Once finished, wake up your Nintendo Switch.
7.- Go to Settings.
8.- Select Internet.
9.- Select Internet Setup
10.- Choose SWITCHWIFI network.
11.- Try to connect.
12.- When the connection fails touch on Continue.
13.- In the new window, choose, only for the first time, INSTALL option.
14.- When it crashes, which is completely correct, reboot your device.
15.- Repeat the steps, but next time choose RUN instead INSTALL.
16.- Follow screen instrucctions.
17.- When the last popup dialog appears saying you have to close that window, click OK to Close it.
18.- Wait for 5 seconds and press once the home button in the joycon.
19.- Apparently it won't respond. But it's ok. It will do it in 6 seconds more or less.
20.- Once in the home screen, select Album again. You should see Homebrew screen.
Nintendo Switch looks to be some issue when password is enabled in Wifi ESP8266 chip. I recommend not to set password while issue is fixed. If you already setup a password you have to reflash the firmware again to clean it.