Steps to upgrade Time Zone version to 26 for 12.2 database.

Please follow the below steps to update the timezone to 26 for 12.2 database.

conn / as sysdba
purge dba_recyclebin;

EXEC DBMS_APPLICATION_INFO.SET_CLIENT_INFO('upg_tzv') ;
alter session set "_with_subquery"=materialize;
alter session set "_simple_view_merging"=TRUE;

exec DBMS_DST.BEGIN_PREPARE(26);

SELECT PROPERTY_NAME, SUBSTR(property_value, 1, 30) value  FROM DATABASE_PROPERTIES WHERE PROPERTY_NAME LIKE 'DST_%' ORDER BY PROPERTY_NAME;

TRUNCATE TABLE SYS.DST$TRIGGER_TABLE;
TRUNCATE TABLE sys.dst$affected_tables;
TRUNCATE TABLE sys.dst$error_table;

set serveroutput on
BEGIN
DBMS_DST.FIND_AFFECTED_TABLES (affected_tables => 'sys.dst$affected_tables', log_errors => TRUE, log_errors_table => 'sys.dst$error_table');
END;
/

SELECT * FROM sys.dst$affected_tables;
SELECT * FROM sys.dst$error_table;
EXEC DBMS_DST.END_PREPARE;

SELECT PROPERTY_NAME, SUBSTR(property_value, 1, 30) value FROM DATABASE_PROPERTIES WHERE PROPERTY_NAME LIKE 'DST_%' ORDER BY PROPERTY_NAME;

conn / as sysdba
shutdown immediate;
startup upgrade;
set serveroutput on

SELECT PROPERTY_NAME, SUBSTR(property_value, 1, 30) value FROM DATABASE_PROPERTIES WHERE PROPERTY_NAME LIKE 'DST_%' ORDER BY PROPERTY_NAME;

purge dba_recyclebin;

TRUNCATE TABLE SYS.DST$TRIGGER_TABLE;
TRUNCATE TABLE sys.dst$affected_tables;
TRUNCATE TABLE sys.dst$error_table;

EXEC DBMS_APPLICATION_INFO.SET_CLIENT_INFO('upg_tzv')

alter session set "_with_subquery"=materialize;
alter session set "_simple_view_merging"=TRUE;

EXEC DBMS_DST.BEGIN_UPGRADE(26);

SELECT * FROM sys.dst$error_table;

SELECT PROPERTY_NAME, SUBSTR(property_value, 1, 30) value  FROM DATABASE_PROPERTIES WHERE PROPERTY_NAME LIKE 'DST_%'  ORDER BY PROPERTY_NAME;

SELECT OWNER, TABLE_NAME, UPGRADE_IN_PROGRESS FROM ALL_TSTZ_TABLES where UPGRADE_IN_PROGRESS='YES';

shutdown immediate
startup

alter session set "_with_subquery"=materialize;
alter session set "_simple_view_merging"=TRUE;

set serveroutput on
VAR numfail number
BEGIN
DBMS_DST.UPGRADE_DATABASE(:numfail, parallel => TRUE, log_errors => TRUE, log_errors_table => 'SYS.DST$ERROR_TABLE', log_triggers_table => 'SYS.DST$TRIGGER_TABLE', error_on_overlap_time => FALSE, error_on_nonexisting_time => FALSE);
DBMS_OUTPUT.PUT_LINE('Failures:'|| :numfail);
END;
/

SELECT * FROM sys.dst$error_table;

VAR fail number
BEGIN
DBMS_DST.END_UPGRADE(:fail);
DBMS_OUTPUT.PUT_LINE('Failures:'|| :fail);
END;
/

SELECT PROPERTY_NAME, SUBSTR(property_value, 1, 30) value FROM DATABASE_PROPERTIES WHERE PROPERTY_NAME LIKE 'DST_%' ORDER BY PROPERTY_NAME;

SELECT * FROM v$timezone_file;

connect / as sysdba
SELECT VERSION FROM v$timezone_file;
select TZ_VERSION from registry$database;

conn / as sysdba
update registry$database set TZ_VERSION = (select version FROM v$timezone_file);
commit;