Your looking for something to edit the swf, right?
Outside of an adobe program, there are a few other paid programs like, Sothink SWF Quicker. To be honest with flash being dead the game would really need to be rebuilt from the ground up, in something else.
A few other things:
Also is noone ok with you continuing his work? Different from making your own game inspired by his.
Someone else already built a tool kit in unity to make a similar game inspired by noone’s game. Edit: The following by the way is not noone’s fatty text adventure.