Sooner or later every witch comes to the point where you think: Hmm, that spell was total crap. Or: I don't actually need this spell anymore.
And then you might ask yourself: Can you also undo spellwork?
yes you can
The how, however, depends on the type of initial spell. If it is a Spelljar or something similar, you can simply dispose of it or disassemble it carefully and clean the elements used energetically and use them again.
If you have energetically charged a talisman or similar object for a specific purpose, you can also clean it energetically and press “reset”, so to speak.
With energetic spellwork like candle spells, it depends on what the original spell was aimed at. Then you have to consider what kind of counterspell goes with it. For example, if you have a love/attraction spell that constantly has unwelcome suitors, you might need to cast a dispelling or cordcutting spell, or cast the original spell exactly backwards as a reversal spell.
Since the latter is incredibly complicated, ALWAYS think carefully BEFORE casting a spell. Consulting Divination is always very helpful. That way you don't get yourself into an awkward position in the first place ;)