On PC/Mac you can continue where you left off while on android you can update the game version automatically but if that isn't the case you can make a backup of your save files.
They can be found here: Android: SD:/Android/data/com.{gamename}*.program/files/saves Alternatively, you can use the file manager to find the correct save map where the Renpy save files belong.
Another easy way is just to ask on discord for a save file, I or someone else can always send you one if you've lost your progress.
Have a nice day.