When I import the .zip file, a message pops up saying: “corrupt file”

Try deleting the file you downloaded and then go back to download it again. When you try to import that newly downloaded copy and it gives you the same issue, then you will want to reach out to NinjaTrader Support for their team assist in the matter.  They have the tools and experience to decipher the issue, troubleshoot the matter and find a resolution. They can be reached at >> https://ninjatrader.com/ContactUs