How can I block my cellphone if the other person have the password

Which password are you referring to, Ivana?

If you are referring to the passcode that is used to get to the Home Screen, then you can change that passcode by using the Settings app. Open Settings ➔ Face ID & Passcode ➔ Change Passcode.

If you are referring to the Apple ID's Password, then you can change the password to your Apple ID. Open Settings ➔ Apple ID (Your Name at TOP) ➔ Password & Security ➔ Change Password.

Axel F.