The question author adding a "conclusion" is a bit of an odd thing that does not naturally fit in Q & A format.
Nevertheless, on the odd occasion the question author strongly feels this sort of addition is necessary, and obviously benefits the site, the conclusion must go in an answer not in the question.
In the same way that people edit answers out of ...
If you can improve an existing post while respecting the original author's intent, you should make (or propose) that change via an edit. As question author, you have a little extra "moral authority", in my view.
More generally, if the answer is genuinely Not An Answer, but could be made so with an edit, consider doing that as well. The best action in each ...
A possible reason for this is explained in the FAQ on Meta Stack Exchange
There are some differences, though, that exist in order to ensure everyone gets a fair shot at answering
Users are less likely to write an answer to questions which already have an accepted answer. You might be satisfied (and rightfully so!) with the answer you wrote, but we're ...
The Help Centre has:
You can also accept your own answer, but you must wait 48 hours to do so. After all, someone else may come along with an even better solution to your problem!
That link leads to the blog entry Jeff Atwood wrote on the subject.
Now, there are some special rules around owner-accepted answers, to
Wait 48 hours. You must ...
The idea of accepting multiple answers has been suggested multiple times on meta.SE, and always declined or found lacking community support. Nevertheless, there is some very useful guidance on resolving the underlying issue.
For example, in Which answer do I accept if I have multiple correct answers? the top-scored answer by Bill the Lizard says:
If the ...
From the Help Center (emphasis added):
What does it mean when an answer is "accepted"?
Accepting an answer is not meant to be a definitive and final statement indicating that the question has now been answered perfectly. It simply means that the author received an answer that worked for them personally.
Understandably, both suggestions can ...
I think that although both answers are correct, you should choose one of them as the best answer.
Obviously, if you are the original poster, you can point it out in comments or by editing the answer, and add a comment about the second one.