Use the theorist's last name and first initial (and middle initial if know) in quotes in an Author search in the advanced search in CINAHL:
You can also click on any author from within an article record to do a search. You may get slightly different results, so it's often best to try both. If the author has a common name, add a keyword or phrase relating to the theory in the second search box.
Use the theorist's last name and the name of the theory (or keywords from the name of the theory) as your search terms.
If you get too many results, you can add "theory or model" in the third box.
Some of the more famous theories have official subject headings, which means you can click on the heading (from the article record--the page with the abstract) and do a search for the theory.
Both CINAHL and Medline have a Subject Heading for "Nursing Theory", which covers articles introducing theories, testing theories, and comparing theories. These articles (and book chapters, etc.) include works by the authors of the theories and by others.
The following link will go to a search for that Subject Heading in CINAHL. You can add additional terms to the search within the database in the additional search boxes at the top: "self care", "caring", "middle range", etc.