If you need to work on a project on a computer that doesn’t have Scrivener 3 or Scrivener for iOS, you can export it to the Scrivener 2 format (compatible with Scrivener 2 for Mac and Scrivener 1 for Windows).
1. Open the desired project and go to File>Export>as Scrivener 2 Project.
2. Choose a name and location for the file, and click Export. To avoid confusion, I’d give the file a name that makes clear that it’s a Scrivener 2 version (e.g. MyAwesomeBook-Scriv2.scriv).