If you are looking for a solution that helps to merge and delete duplicate Outlook contacts, then you can go with the FreeViewer Outlook PST Merge Tool (https://www.freeviewer.org/pst/merge.html). This software works the PST file of Outlook 2019, 2016, 2013, 2010, 2007 and other versions.

It allows the user to combine and delete duplicate entries in Outlook contacts (https://www.freeviewer.org/blog/combine-delete-duplicate-entries-in-outlook-contacts/) without loss of data integrity. The tool supports to merge multiple PST files into a single file with all emails, contacts, and calendars.