Scrivener 1 with Windows, Scrivener 3 with iOS, and Dropbox

Need some help finding clear instructions. I’m primarily using Scrivener 3 with iOS and backing everything up to Dropbox. I would like to be able to sync to my Scrivener 1 on Windows computer using the same Dropbox folder so I can easily move between devices. Where are instructions to set that up?

There is no Scrivener 3 for iOS, but this should get you going (thanks to Literature & Latte):

or this (mine):