I haven't used Unity before, so I'm open to hints about where to look. Otherwise I'll just slog through and figure it out eventually.
I have no interest in this game but saw this while browsing the comments.
Assuming the transition was written via code (and not by some sort of asset store thing), then you don't need Unity. Assuming this game is structured like every single other Unity game, download dnSpy and navigate to the game's data folder\Managed\ and open Assembly-CSharp.dll with dnSpy.
Then in dnSpy, go to Assembly-CSharp > Assembly-CSharp.dll > - (Yes, a dash. It should have {} as the icon). Then find the code you're looking for, edit it, and go to File > Save Module to recompile the dll.
This applies to most Unity games, by the way.