Oracle 12c SYSTEM user locked out
Ok, figured it out with the comments from my original question. Steps I used to connect to the correct instance and get the account unlocked and password reset.


Connect to the correct SID/instance off the top. Example:

c:\sqlplus SYSTEM/&lt;Password&gt;@&lt;service name&gt; --> this can be found in the tnsnames.ora file
I then verified I was in the correct instance:

SQL&gt;select instance_name, status from v$instance;
From there I was able to unlock the user and reset their password:

SQL&gt;alter user &lt;USERNAME&gt; account UNLOCK;

SQL&gt;alter user &lt;USERNAME&gt; identified by &lt;PASSWORD&gt;;


My problem intially was that I was just trying to connect using sqlplus / as sysdba and it wasn't putting me in the correct instance.

Hopefully this will be helpful to other Oracle devs and rookie DBA's (I'm a rookie in this since we have a dev instance for some client work and it rarely gets touched).