Go through bibliography
Often when you are going through a scholarly journal article or a book, you can take a look in the bibliography to find other relevant sources on the same topic.
It's easy to add these references to Citavi. The quickest way to add references is via the DOI name or the PubMed ID, if they are listed. If that's the case, see Adding Journal Articles by ID.
If the bibliography is available in digital form (PDF, etc.) Citavi can search for the listed references. To do this, see Importing a Formatted Bibliography.