Adding exposure data to film scans is not commonly found in most photo editing applications, because those applications mostly assume the files are coming from digital cameras where all that info is recorded automatically.
But there are a lot of us who scan film and want to add metadata to the scans. People have written utility software to let you do that. On the Mac, a couple of options are:
If you’re comfortable using command-line software, you can use exiftool. Many of the utilities that do this include exiftool code.
However — because you wrote that you are using Lightroom 4.2, if the images you want to edit are already in Lightroom, you probably can’t use the kind of utility software listed above. After you add images to cloud Lightroom they are uploaded to their master storage area on the Adobe cloud servers, and once there, I don’t think there is any way for you to alter EXIF camera metadata. The type of utilities listed above work only on files stored on a locally mounted volume (works great with Lightroom Classic, not possible with Lightroom). If you want to do this with images you already added to cloud Lightroom, you might have to delete the copies in Lightroom, add the info to local copies, then upload the modified copies. Which would be awkward especially if you’ve already been organizing them into folder and albums. I hope I am wrong about that (and that someone corrects this thread if that’s the case), but I think it’s how it works.
So the most practical time to add camera info to film scans is before you import them into Lightroom.
If this was about Lightroom Classic, no problem. After you add camera metadata to a film scan, Lightroom Classic will read in and display that information when you import the images into a catalog; or if the images are already in a catalog, you can make it re-read and update the camera info by using the Read Metadata From File command.