How to update comments in arXiv?
Comments can only be updated by submitting a new version, even if the content of the paper itself has not changed. A new version can be submitted by selecting the &quot;Replace&quot; option against your paper. Further details can be found here.
Comments are a part of the metadata of the paper, and the idea is that the comments should reflect the situation on the date the article was submitted on arXiv. It is possible to update journal reference and DOI without creating a new version. However, as the help page mentions, these fields are appropriate only when you have the complete bibliographic information of the conference proceedings (if any) available.
Reference from arXiv (emphasis mine):

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Why? To allow authors to make changes to the comments and other metadata fields of publicly announced articles without generating a new version, and hence date stamp, would effectively mean that all changes would be backdated to the time the last version was submitted. This is open to abuse and thus not allowed.
The exceptions to this rule are the addition of journal reference and DOI information. The journal reference field may contain only full publication information for the article; the DOI field may contain only a DOI.