Follow these steps:
- Go to Pure: https://pure.knaw.nl
- Go to Master data and click on Journals.
- Under Journals click Duplicate Titles and Duplicate ISSN.
- Check the list of duplicate titles/ISSN.
- By clicking the journal title you can go the journal record.
- Decide which record should be set as target.
- Click on Set as target, Preview merge, and Merge.