When I first started plate solving I was asked to download some star charts. I did a few but they took quite a time ( I am on 4G). The plate solve then worked. However I probably need to download the rest? Where do I do that?? Plate solve has never requested anymore.
Beginer question.

The index files that you require depend on the focal length (Field of View) of your setup/image. The utility for downloading the index files indicates a few that are considered mandatory. You can download additional ones if you want. The smaller scale indexes are quite large. So, if it's not complaining about missing index files, and the solving is working, you don't need them all.