By my research, I found a very closely related word that denotes making something bad even worse, that is exacerbate:
1. make (a problem, bad situation, or negative feeling) worse.
But, I am not fully satisfied with the word exacerbate, as it denotes turning bad into worse. I want the word that denotes turning something good (e.g. mobile, car, computer, etc. working fairly well) into bad while trying to fix something needlessly.
The sentence, in focus, can go something like this:
- He has _____ my computer, which was already working well.
The term destroy (apart from exacerbate) might be another option for me, but it totally connotes the physical harm of anything, rather than the harm in functionality (of computer, mobile, etc).