This method works for desktop/laptops, and, I believe, for tablets in landscape mode.
First, make sure that you are searching in the white oval on the blue bar. (It looks like that is the only search now, but there used to be another.)
Click just to the left of the magnifying glass within the white oval (not right on it) and you will see This Topic with a small downward triangle beside it. Click on the triangle, and it will open the menu to select where you want to search.
Then fill in your search term.