I think I know the answer you are on about, and so I'll state first I'd love to see what you've done, after receiving the review, so that I can improve my answers.
If you can write the comment as an answer
Adding an explanation to an existing post is fine, I've done this before and got more upvotes than the original answer! And another user based the opening of their answer on that answer too. this is the post in question.
It's also ok to post two answers that are very alike. It allows users to have a second perspective on the content. And I know I've never been downvoted when this has happened. (I don't have the time to find an example)
Finally, all an answer needs to contain is one piece of advice that a can help a future person. And adding additional information is more than likely going to do this.
If you cannot write the comment as an answer
If you cannot make an answer from what you learnt on your own, then posting a lot of comments on the answer is the best way to go. After a few comments SE gives users the option to talk in a chatroom and talk about the answer. This can give you an opportunity to write down what you want. And I can't think of a user that would dislike this, we're already helping you for fake internet points, real gratitude is way better.
If you fall into neither of the above
If you don't want to comment or answer than you should follow our help center as best you can.