There are generally two courses of action possible.
If there are no answers which will be invalidated by an edit, then edit the question to make it clear exactly what you are asking about. You can phrase the question in such a way that it cannot be answered by the nominated duplicate. That is, don't say, "This question is not a duplicate of X because I'm asking about..." but instead just make it clear what it is that you are actually wanting to know. By doing that you will eliminate question X.
This is the course of action recommended by the system: you should see an "Edit question" button in the duplicate-question banner.
However, there's also Help on closed questions and specifically on duplicates. This even says "If you see a question and do not agree that it truly is a duplicate, edit it to highlight the differences, then try to get it reopened by casting a reopen vote."
But, if there are already answers which are valid for the question as it's currently written (even though it may not be what you meant when you wrote it), it's bad form to invalidate them. A substantial edit may even be rolled back in that case.
If there are answers which would be invalidated by such an edit, but there are no answers which tell you what you want to know, then ask another question, making it clear exactly what it is you're asking about. You could even reference the first question, saying "I asked question X but didn't make myself clear..."
In the example you link to, the question isn't very clear. You know what you're asking about; but everyone else has only the words you write to go on; your thoughts don't travel well through the ether. The question could say that you're concerned about the redundancy of "on foot" when using the verb walk. You've added that in a comment, so presumably it was actually necessary to state it — it should have gone in the question.
An answer appeared 25 minutes after your question, which actually explains exactly what you wanted to know: on foot is indeed redundant. You've accepted the answer: it's answered the question you actually had (and not the one you wrote).
In this case, the duplicate is irrelevant. You asked a question and you have the answer you were looking for. In this case, the pointer to a duplicate is merely a "See also" for anyone who has a similar question.
It appears that the current duplicate was in fact suggested in November 2015, but failed to get the necessary votes in the required time. That it has come round again is suggestive that the question is not clear.