How to make changes in Oracle Universal Installer?

I don't have an Oracle11 install to look at anymore.  I think the Oracle installer used to use *.xml files in either the install or oui directory of the Oracle_home (or possibly the Oracle_base) to track the installed products.  You may be able to find a *.xml file there that you could edit manually to change which products the installer thinks you have installed.  Make sure that you do a complete backup or at least save a copy of any *.xml files that you may change manually, in case your changes make things worse.

The location of the installation information is stored in the oraInst.loc file.  Unfortunately, the location of that file varies by UNIX variant.  The most popular locations are /etc and /var/opt/oracle.  If it isn't in one of those 2 locations, then you'll have to search for it.

I don't have 11 to look at either, so there could be an XML file, or it used to be this massive directory tree with all kinds of stuff in it.

Honestly, my first try would be to run the installer and uninstall what you are trying to install.  It will fail, but it may update the inventory.  Really, the only way to correct the inventory files is to reinstall.  It had a habit of getting corrupted in the past, and that was always the solution.

The lowest version I have installed right now is 12.2.  Trying to trace the inventory for this is impossible (as it always has been).  The oraInst.loc points to ORACLE_BASE, which has some small file, which points to another location.  That goes somewhere else and has a ton of different stuff in it.  Multiple directories.  Looks like the old directory tree version of the inventory and the XML versions.  I'm not going any further than that.  If you start messing around in the giant rats nest, good luck and you'll likely break something and have to reinstall anyway.

Just FYI - if you break the inventory, the database will still run.  You just won't be able to run the installer.