1. With FTP, create a folder in a website directory
   Example: /domains/xenonis.nl/public_html/test/dbmerge/
2. Save the splitted database backup files into that folder.
3. Save the manualFixForUnjoinedFiles.php file into that folder.
4. Open your browser and enter the site home page URL + /dbmerge/manualFixForUnjoinedFiles.php?run=fix
   Example: https://test.hrcws.nl/dbmerge/manualFixForUnjoinedFiles.php?run=fix
5. Press enter.
6. The process will be displayed on the screen; please wait till browser loading completes. It can take some time based on how many files need to be joined.
7. Once the browser loading is completed, check the folder where you will find the merged file. Now it should be back to the original position.

Source support ticket: https://support.infinitewp.com/support/tickets/105546