Note: Save transfers are only compatible if both devices are running the exact same version of the game. If your PC has received a major content update that mobile has not yet received, the transferred save file will not load on your phone until the mobile app updates. Troubleshooting Common Save Issues "My Farm Disappeared From the Load Screen"
Before you can back anything up, you need to find where the game stores your farms. The location of your varies depending on your operating system: save data stardew valley pc updated