Someone posted an incorrect answer, I pointed it out, they edited the answer so it is now correct and my comment is no longer relevant.
What is the etiquette: should I remove my comment or post a new one saying "Ok it works now"?
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Yes, remove your comment. Comments are temporary by design and when they have been addressed, they should be removed.
Comments are temporary "Post-It" notes left on a question or answer.
Once you do that, the author of the answer knows you're satisfied with the new solution. It is even conceivable that after updating their answer, they will flag your comment as No Longer Needed and it might be deleted before you can do it yourself (don't worry, this doesn't carry any penalty for you at all).
Please don't post something like "Ok it works now"; upvote and/or accept the answer, which is the Stack Exchange way of saying something works/is useful.