My keyboard is old and it caused me to accidentally mark an Anki card right when I actually got it wrong. I don't want to "forget" the card; I just want to change today's result to "wrong" and let the SRS algorithm put it where it belongs. Is this possible?
I would recommend ignoring what happened. Let it go.
When the card comes up the next time, either you get it right (maybe you have learned the contents meanwhile from elsewhere) and thus the mistake you now did turns out to not be serious, or you get it wrong and it comes up again the next day, in which case this has simply been postponed by a bit. But this is unlikely to have any long-term effects in any case.
The spaced repetition system is robust against random noise in this way, regardless of the source, since the cards come up eventually again and then the system self-corrects.