You can't. It's one of this website's biggest flaws.

The absence of an EDIT feature is a major failing on the italki website. For example, when one presumes to teach others, and you type a "correction" with typological errors and so forth, one ought to be able to correct it for the sake of the student. Instead, it is necessary to type a second message, indicating your typing mistake. .

I absolutely agree that this is one of many flaws in italki. I was going to write "design", but I tend to think that italki began without much software design. I also think that the lack of supported editing tools is another flaw (feature?). Let me try bold.

Old question, but I'm still wondering this myself. Maybe italki wants to keep the traffic that comes through original posts? Thanks.

When I joined italki, it had an edit button. But since the format changes, the edit button is no longer available. What a shame!