Well I can explain how it works on my Mac; I’m pretty sure Android and Windows work the same.
Basically there’s a folder in your computer which contains all your Being a DIK saves. I have many runs; monogamous runs for Isabella, Jill, Josy and Maya, Sage, Quinn, Riona, Nicole, Lily, Jade, Cathy, Nora, Josy only, Maya only, Zoey, and nobody; plus a fuckboy route which avoids monogamy. Plus variant routes where my MC is more of a DIK or more of a CHICK. Plus new routes my girl and I are doing together.
Plus, for convenience, I have save points throughout the game so I can visit certain scenes in different runs. If I wanna see the MC take Cammy and Riona to the Haunted Mansion escape room, I can; if I wanna see him take Jill to it, or Bella, or Josy and Maya, I have that too.
And every time I complete season 2, the app tells me to save the file so it can be transferred to the next season. Then when I open the season 3 app and select “Continue,” it taps that folder, shows me all the files from the end of season 2, and imports the file I select.
The season 3 app has its own folder for its saves, but it still looks at the seasons 1-2 app folder for the imports.