how to reply to posts on google groups (and not reply to just author)

[davidj411]

I want to reply to the goups and not author for  an older post (from
February) , but it seems i can only reply to the author (using google
groups).

 Is there a way (within Google groups) to reply to an older post to
keep that particular thread going instead of posting a new one (as i
am here now doing - sorry about this being a non-python question.)