never tried myself but I think is simple as contacting support (with no DMCA) and point them to the original and the rip off item.
If you are not the author of the original author you can’t send DMCA. You can also contact the original author, he will probably send that DMCA request for himself.
There are many items so reviewers may miss some obvious duplicates, contacting support will help them pin point the issue.
I see items taken down and some time authors banned and even if we don’t know the details behind, it appears they take actions against copyright infringements.
In the end, what we consider a duplicate, for the staff could be a genuine product.