We are FETtec and create and sell high quality drone parts for hobby, sports and industry.
KISS is a firmware/product owned by the company Flyduino.
Our product FETtec KISS FC is a Flightcontroller with FETtec hardware and KISS based software.
The FETtec 4in1 ESCs (35A/45A) are our own products with hardware and software from FETtec.

KISS FC / FETtec KISS FC has to be set up and flashed with the KISS GUI https://github.com/flyduino/kiss-gui/releases.
FETtec products have to be set up and flashed with the FETtec Configurator https://github.com/FETtec/ESC-Configurator/releases/tag/0.1.31..

Always test the electronics via USB before building the quad. (FC connection to ESC via 8pin cable which comes with).
Be sure to close KISS GUI before opening the FETtec Configurator.

Read the manuals https://fettec.net/download/ and follow them.