Most people who have the need to create custom reports use the Published Views feature. This exposes the Dimensions CM data in easy to consume views on top of which queries can be created to support your custom reporting needs.

Ideally, your Access DB was being populated by first querying the Published Views. You may have had links or pass through queries in Access to query the data directly from Oracle (hopefully through these published views). If you can still access Access to see the different Reports and Queries created, you will at least have a foundation upon which to migrate to a different tool.

There are plenty available. I have seen people use Crystal Reports as one such example.

General link to Published View help (follow to get to pdf)

https://admhelp.microfocus.com/dimensionscm/en/14.5.2/online_help/Content/UserHelp/reports.htm

Dimensions CM also has a built in Report Builder that may support your needs. See these help topics depending on your client.

https://help.serena.com/doc_center/cm/ver145/desktop_client/desktophelp/reportbuilder/about_the_dimensions_cm_report_builder.htm?zoom_highlight=published views

https://help.serena.com/doc_center/cm/ver145/web_client/webclienthelp/reportbuilder/about_the_dimensions_cm_report_builder.htm?zoom_highlight=published views