On the home page, simply search for the item that you're interested in.
Once the search result is shown, select “FOLLOW THIS SEARCH”
Once you click "FOLLOW THIS SEARCH", the blue link will turn white and update to "FOLLOWING SEARCH". This means you have successfully saved the search term.
You can view your saved searches by going to "For You" on the top right corner of the page or by clicking the "Hi, Name" dropdown. On the dropdown, click "Followed Searches". Your saved searches can be found in the "My Searches" tab.
On the mobile app, the saved searches can be found in your "Favorites" which is located on the bottom toolbar. Once you click "Favorites" make sure to go to the "Searches" tab.