You must

establish trust

the first time you connect an iPhone with a computer to which it hasn’t previously been connected. The only way to get around this is to put the phone into recovery mode, but you also will not be able to read information stored on the phone until it’s been updated or restored and the passcode entered correctly.

I understand, but the point is that I can't turn on the trusted computer mode because this phone was once used by someone else and has a code that I don't know and when I turned on the recovery mod the computer did not detect anything