Updating the application: manual section without content

We are currently trying to update from GNOS 3.6 to 3.8. Unfortunately the DB then "disappears", i.e. data do not show up in 3.8.

Looking at the documentation:

"Updating the application"
- https://geonetwork-opensource.org/manuals/trunk/en/maintainer-guide/updating/index.html
- https://github.com/geonetwork/doc/blob/develop/source/maintainer-guide/updating/index.rst

... does not have _any_ content.

Please document how to do upgrading (or add pointers to existing documentation elsewhere). Thanks!

Read source/maintainer-guide/updating/index.rst and the linked “Updating the application” manual page first. Research the GNOS 3.6-to-3.8 upgrade process and document it there, or add pointers to existing guidance, including the database/data visibility problem. Done means the section contains usable upgrade instructions or clear links to them.

Written by the indexing model from the issue text.