Usually when this happens, you need to uninstall and install...
To prevent losing the save files, do this:
I downloaded the game in computer as well just in case:
Computer:
Your saves folder will be at: Game folder > Game > Saves
Android:
Open the file explorer (files app, or any name like that) or via your computer... Works as well!
Go to the following folders:
Android > data > com.andehpi.ac > files > saves
(Pretty much every VN (and app) have the same way to save the files, you'll just need to find the main folder that's the "com.andehpi.ac" that will be another one for each app...)
Some folders can be hidden, so try to see if there's an option to see hidden folders if you can't find anything :D
For the back up: (the idea is the same for both systems)
- Copy the saves folder into another folder where you want to have the back up
- Uninstall the old version
- Install the new version
- Paste the backup in the same folder (saves folder) you have inside the new installation
If you still have any trouble, please reply and I'll try to help!