I wrote that FAQ article eelik pointed you to.
That article is not going to help you much. In that FAQ article I simply deleted all footprints and replaced them with footprints from KiCad’s libraries.
I am surprised that all SMT pads are converted to via’s. Doing so for the holes in THT pads is “normal”, because the concept of “pads” does not exist in many Gerber files, and therefore Gerbview can not do much more then convert them to via’s.
Creating a KiCad project from Gerber files is far from ideal, and an excessive amount of work if your intentions are only to change some small things. The ideal tool for that would be a Gerber Editor (Instead of a Viewer). This old Eevblog thread has some links to gerber editors: https://www.eevblog.com/forum/eda/gerber-editor/
Editing your drill files with a text editor as eelik suggested may be a valid option. Depending on what you want to do, it may be as simple as changing a single number for the diameter of a specific drill.