i need to unlock my iphone

After you erase / reset the phone, you can use a current backup during the new setup to make your phone look just like it did before you forgot the passcode.

For the future, it might be a good idea to write down important passwords and keep them in a safe place.....even though you might feel that you will never forget the passcode.

If you mean you forgot the passcode or the phone is disabled or displays "unavailable", you don't. Your only option is to erase and restore the phone.