Could explain a bit more about what you are trying to do? The "People" section is automatically populated with all the faces that have been detected by the face recognition software. All faces that have been named, and all unnamed faces that contain at least five instances of the same face, will appear in the People section. It's not possible to manually draw a face recognition frame that the software did not detect, is that what you are wanting to do?
When I add new pictures (new people) to my photos file they appear in the photo display. however, they do not appear in the people display. How do I get the sw to rescan the photo file so that the new pictures are added to the people section?
The first thing to do is to check that the People view is enabled (it is by default, but can be disabled by the user). Open Preferences>General tab and ensure the option is enabled.
Assuming it is still enabled, there are two reasons why you may not be seeing a face in the People section:
1. The face recognition software has not recognised the face as a face (e.g. profile shots). If it hasn't recognised a face, there is unfortunately nothing you can do in Lightroom to manually draw a face recognition region. So unrecognised faces will remain untagged.
2. As I mentioned earlier, a recognised but unnamed face will only appear in the People view when there are at least 5 instances of that face. However, if there are less than 5 photos with the same unnamed person, they WILL appear in the People section if you are able to name them.
So, if you select an image that has a face or faces that you know, but which isn't showing up in the People view, then open the Keyword tab (near the bottom of the right-hand toolbar), you will find a People section showing above the Keywords section in the right-hand panel if there are any recognised faces in that selected photo (named or unnamed). If the face is unnamed you are able to type in the name if you know it (and once named, it will then appear in the general People view). If there are multiple faces on the same photo, and you want to make sure you're adding the correct name, you will find that if you hover the cursor over any of the faces in the list in the right-hand panel, a white rectangle will appear over the corresponding face in the image (but you must be in Detail view, not Grid view, for that function to work).