ALM Global Search is part of ALM/QC, but generally requires an ADDITIONAL server to do it as it is compute intensive and will slow down the ALM server if installed on the same machine.
Also, it could be a bit cumbersome to implement for little gain as we have heard from customers. Generally, most customers say it is not worth the added effort, overhead (cost/server/RAM/CPUs/Disk/ALM-user).

It REQUIRES 16Gb (32 recommended) and a HUGE amount of Free disk space (Ratio of 1:5 between the size of the ALM database and Global
Search. For example, if your ALM database is 20 GB, then you need at least 100 GB of free disk space for Global Search.)
It also requires a DEDICATED ALM User, so if you have "named" licenses, or a small number of "concurrent" licenses, it will always claim one.
The OLDEST version available on the MF Marketplace is for ALM/QC 12.6, so you might  need to upgrade your ALM to use it.

Here are some links to how to enable it:
https://admhelp.microfocus.com/alm/en/15.0-15.0.1/tools/Global_Search/Global_Search_install_guide.pdf
https://marketplace.microfocus.com/appdelivery/content/alm-global-search (it is ALM version - specific)
https://admhelp.microfocus.com/alm/en/15.0-15.0.1/online_help/Content/Admin/sa_enabling_GS.htm?Highlight=global%20search
https://admhelp.microfocus.com/alm/en/15.0-15.0.1/online_help/Content/UG/t_global_search_alm_data.htm

There is also a DB-side text-search capability (CTX in Oracle, and Text-search in SQL-Server). It needs to be enabled on the DB-side and can speed up search on most memo fields.
This is generally what customers try INSTEAD of Global Search.

https://admhelp.microfocus.com/alm/en/15.0-15.0.1/online_help/Content/Admin/sa_textsearch_configure_toc.htm?Highlight=text%20search
https://admhelp.microfocus.com/alm/en/15.0-15.0.1/online_help/Content/Admin/sa_textsearch_enable_on_db.htm