While doing upgrade from oracle database 12.2 to 19c, we need to do the upgrade apex as per preupgrade recommendation
Upgrade Oracle Application Express (APEX) manually before the database
The database contains APEX version 5.0.4.00.12. Upgrade APEX to at least version 18.2.0.00.12. Starting with Oracle Database Release 18, APEX is not upgraded automatically as part of the database upgrade. Refer to My Oracle Support Note 1088970.1 for information about APEX installation and upgrades.
you can able to download older apex too.
Unzip apex software
move older apex version directory to somewhere and copy the apex to oracle 12c home path.
From command prompt, go to apex directory location and then execute the following command from sql as sysdba
before that , you need to know
There are two types of APEX installations: development and runtime only. To determine which type is currently installed, run the following query:
select count(*) from <SCHEMA>.WWV_FLOWS where id = 4000;
<SCHEMA> — curent APEX schema Example APEX_5000
If the query returns 0, it is a runtime only installation, and apxrtins.sql should be used for the upgrade. If the query returns 1, this is a development install and apexins.sql should be used.
As administrator command prompt
@apexins.sql SYSAUX SYSAUX TEMP /i/
It will take sometime to upgrade