Firstly, thanks for the answer.
The first method I was trying was to remove the secure thing from the FPC tape, then put ohmmeter probes between pin 1 and 2, then move the second probe from pin 2 to pin 3, 4, 5 and so on, before every probe move i was trying to press every button and check for connection, just like in casual matrix keypad but as I said it gave no results.
Now i attached the probes like on the image:
Normally the ohmmeter shows about 20M Ohm, when i press some buttons it drops to 5M Ohm, but I'm not sure if it's measurement error because i need to hold the paper upside-down. I probably need an FPC connector to get reliable results.
Am I measuring it in wrong way?