Hi Niels,
how to run touch sensor tests is decribed here - it will work both for BL-touch and CR-touch sensors: https://www.3dprintbeast.com/bltouch-self-test/
You’ll need a tool like Pronterface (Freeware) to initiate the mentioned G-Code test commands via USB connection from your computer.
If the touch sensor is still not working you may want to try the trouble shooting instructions suggested in the following link [Caveat: I won’t recommend changing firmware before being sure that there is no mechanical or electrical/wiring problem present]: How to Fix Auto Leveling Sensors Not Working - BLTouch & More - 3D Printerly
Additional documentation can be found here:
https://3d.nice-cdn.com/upload/file/BLTouch_Manual.pdf
Greetings
Bjoern