Your task #1 is to find the coms.
@Nick I think OP meant it wasn't actually that model, but a 10-pin-per-side similar one
The site where I bought the display does not show any description, brand or model about it.
No idea how to do it
QuoteNo idea how to do it Use your arduino to generate a (roughly) 100hz signal. Take the GND (or VCC) pin and the signal pin, and apply them to any two pins on the lcd.As you slide around the signal pin, and see lots of segment liting up, the GND pin is on a com.
think about only 2 pins on an I2C controlled display like these: