Short answer: iOS Scriv has an export function. For two way transfer the exchange lists using iTunes, but in the current day, that would be handled by opening a Finder window onto your hitched up phone and looking under Files.
Of course, this is not a “sync” option – which you still seem to want. Rather, it is strictly Scriv project file transfer. So, you would be engaging in the dangerous practice of moving the project file back and forth and overwriting what was previously there.