Once in the Classic Catalog, click the link to Advanced Search:
In the Advanced Search screen, there are two things to do to find theses or dissertations from a program.
The graduate major and concentration will be listed in the Notes for the thesis/dissertation record. To search that, change the dropdown field before the first search bar to "Note:" then enter the program into the search bar.
To limit to theses and dissertations, scroll down to the heading "Add Limits (option)" and change the "Material Type" dropdown menu to "Thesis/Dissertation."
All of your results should not be theses and dissertations, and if you look at the Notes section of each record you should see your search terms.