Hello! Yes, you need to redownload the game (make sure you are playing version 1.2.3 of the game, you can look it up in the "About" screen).
About replaying the whole thing from the begining... That is up to you 😊 We just recommend to start over because old saves usually end up causing bugs. Actually, in this version, we already found out old saves don't show the character's affinity percentage properly on the stats screen 🥲
We hope you enjoy the new content! 💕