Before the PubMed interface was updated in 2020, the search details were in plain view on every results page. Now, however, you need to dig a little further to find them, and they're not as easy to update.
In the Advanced search window, beneath the query box, you will find a History and Search Details box. Toggle open the Details for a particular search to show the details of exactly how PubMed interpreted your search query. The image below shows how the blood draw babies query was mapped.
With the search details, you can:
The Search Details can be edited by copying and pasting the query (above Translations) into the query box and editing there. Because of the nesting—represented by parentheses—this can be a bit of a challenge to do correctly! The search illustrated above brought up some results that didn't quite hit the mark, so a few terms were removed and the search was rerun as shown below. (Note the number of results decreased from 2,395 to 2,021.)