How can I change or set the SYSBDA password for a firebird 3.0 embedded database.
I don't/can't want use the local or default authentication.
This is basically a duplicate of your previous question. Firebird Embedded doesn't check passwords at all, so changing passwords is irrelevant: it will have no effect on using Firebird Embedded, because any password is accepted as valid.
That said, if Firebird Embedded is configured to have a UserManager (which, judging by your previous question, is not the case in your setup), it can be used to change the password in the security database using ALTER USER <username> SET PASSWORD '<newpassword>'. Doing that, however, has no effect for Firebird Embedded itself as it doesn't check passwords, it only has effect for connections connecting through Firebird Server using that security database.