I haven't stated this one but normally you just install the new apk while the old one is still there. It will realize it's a newer version and install as a update. However if this is anything like the other games they released echoproject then you can't update and unfortunately just got to delete the game along with its save data and install the new one and start from the beginning. This is what I did with there last game and eventually I just stopped and waited for it to be complete. Unlike other projects though these don't take as long to complete aside from echo but I stopped caring about that game when Flynn meet his unfortunate end with no way to help him.
many cheraters in these games start out kind of a butt. It's when you help them deal with there problems when they get good and you do start to help flynn with them a little before he you know what ever you can call what happened to him happened. It may not have been with the MC but he was getting better. I'm also used to the idea of a Visual novel only having a bad end when you do something wrong so when I got his end I searched the comments to find out what I messed up and found that no it's all supposed to happen and that just annoyed me. So I just never bothered with any other route. I never even looked at smoke room because the same thing is probably going to happen in that. I'll get attached to a cherater then will have a bad I never played the other routes but the others all seem to have some kind of good or neutral end but flynn just has this one bad one. It doesn't really seem fare for the players that may have liked him. Plus he's scaly in a fandom over run by wolves and fox people I like to play the games with scales.