How to connect online-Nextcloud with a NAS

I have a problem. I want to connect my NAS (Asustor) with my online-Cloud of Nextcloud (Server is AllInkl).

Is there a possibility to do it. With the App NextCloud for Asustor I just can make my NAS as Cloud, but this isn’t what I want.

Unless the NAS can run Nextcloud (and you can federate the two), the best idea is probably to open ports on your firewall to allow the online cloud to add the NAS as external storage.