Open the active game save folder ( .../Feed and Grow Fish/SavesDir ).
Notepad (built-in Windows) or Notepad++ (recommended for clean formatting). Step-by-Step Editing Guide
Install Feed and Grow Fish on the new computer via Steam and launch it once to generate the default directory structure. Close the game completely.
If your fish dies or your save becomes corrupted, simply copy your backup files and paste them back into the original SavesDir folder, overwriting the current files.
If you play the game but your progress isn't saving:
Sometimes data is stored in the local app data folder: %LOCALAPPDATA%Low\OldSoftware\Feed and Grow Fish 2. Steam Play (Linux/Proton)