It's actually a verb, "Verschlimmbesserung" is the substantivization.

Base: verschlimmbessern

Present conjugation: I verschlimmbesser[e], you verschlimmbesserst, he/she/it verschlimmbessert, we verschlimmbesser[e]n, (plural-)you verschlimmbessert, they verschlimmbesser[e]n

Past/perfect: verschlimmbessert (e.g. "it got verschlimmbessert")

Imperative: verschlimmbesser[e] (e.g. "don't verschlimmbesser that!")

The [e] at the end is leftover from an older form, in the cases where I omitted it it would sound archaic to a German speaker, but in the other cases it's equivalent or may even sound better. It's also regionally different. The archaic versions kinda sound south German (Swabian, Bavarian).

[ed. made some adjustments]

P.S.: "Verbesserung" means improvement, "Verschlimmerung" means worsening/aggravation. The combined word is understood quite specifically though, not just as a combination of the two. It's *not* a normal case of German "paste words together", that's for nouns (you can do it with the substantivization, e.g. Donaudampfschiffverschlimmbesserungskapitän = "captain of verschlimmbessern the steam ships on the Donau", which makes little sense of course). It's not identical to enshittification either, the latter (to me at least) implies intention; verschlimmbessern you can (and probably often will) do by accident.