changing the code on a cd-disk bought game

so im not really sure if this is the right place to ask this. if not, please say so, and if you know where to ask feel free to send me there.

I recently bought an old school game (mijn dierenkliniek, a belgium/dutch game) that i played a lot during childhood. however, it seems like it has some bugs that i find really annoying. i am not an amazing programmer, but if the code isnt spaggethi coded i can usually read it and make tweaks. problem is, i have absolutely no clue how i can acces the code, let alone change it in a way where i can test it by having 2 versions (1 original version and 1 with the tweaks)

if there is anyone who could help me, thatd be amazing!

(also, no wonder i wasnt able to defeat this game as a kid with all these bugs. it's really annoying to play that way and knowing how i was when things just didnt go how they where supposed to i probally ragequit more then once)