I checkmarked the wrong answer here. Is there any way I can change it?
If you put the green checkmark on an answer by mistake, you can always change it:
- either by re-clicking the checkmark on that answer, which unaccepts it,
- or by clicking the checkmark on another answer, which accepts that one and unaccepts the first one.
Nobody else can affect the checkmarks on answers to your question. Acceptance is the prerogative of the question asker only. So judging from your comment, you must have unaccepted the wrong answer without realising it, perhaps by accepting another answer instead.