Enter a search term in the Libraries Quick Search Box, and leave the Search Options set to Primo
On the search results page, look on the left-hand side of the page for the Resource Type link. click on the arrow next to it to expand the list, and select Books.
On the next page, look again on the left-hand side of the page for the Collection link. Click on the arrow next to it to expand the options, then click on the Hathitrust Digital Library Full View link
On the next page, look for the Available Online link in a title you are interested in. Clicking on this link will take you to this item in HathiTrust.