Since you're already aware of the accurate and inaccurate parts of the post, I trust you want to take action to help improve the answer and assist others who might rely on it to solve a similar situation. Therefore your options are:
Leave a comment explaining what you believe is wrong. If you're able, include a suggestion on how to improve the post. This helps the answerer improve their post and alerts others to the possibility it contains wrong information. The answerer or other users can consider your comment and provide feedback. If you find there was a valid reason for the statement and your comment is no longer needed you can delete it. Conversely, if your comment leads to an improvement to the answer rendering it obsolete you can delete it. Only moderators can see deleted comments.
Vote. If you feel the wrong information outweighs the good, consider a down vote. You may also find the answer useful despite the questionable statement and wish to up vote. It's really up to you. Voting is important though because it shares your expertise with future visitors who may not be as easily able to identify the correct/best solution to the question.
Actions to avoid
Because the answer is a legitimate attempt to answer the question you should not flag it. Editing it is also not an option as it's clear the poster intended to make the statement in question.