How to reset xbox 360 family passcode offline

If this is about the family settings passcode, you can
reset that Xbox 360 family passcode yourself, if you have an adult account with these instructions.

How to reset family passcode

Here is a link to the support article that will tell you the steps on how to reset the family passcode on your 360

https://support.xbox.com/en-US/xbox-360/security/forgotten-parental-controls-pass-code

You can reset the family passcode if you have an adult Microsoft Account, and the console is registered to that adult account. If so, you can simply
follow the instructions here to reset the Xbox 360 Family Safety passcode.

If you've forgotten your Xbox Live gamertag's passcode you just delete and redownload your profile. This will clear the profile of any passcode. Now, if you've forgotten your XBOX 360's Family passcode then you need to contact phone support, there's absolutely
no way to reset it manually by yourself without speaking with phone support. Worst case scenario is that you will have to "Reset to Factory Defaults" to clear the forgotten Family Passcode.

I don't believe even a factory reset will clear a lost family passcode. You would have to contact Support for that.