"This can be done locally or over SSH" ... how to do that if the Pi-hole is installed on my AsusNAS ?
Login to your AsusNAS via shh, and then enter the command as telekrmor has detailed.
You haven't provided any details how you installed Pi-hole on that AsusNAS, but in case you'd happen to run your Pi-hole as a Docker container, you'd have to run that command from inside the container.
This sounds very complex ! I just reinstalled the app !! Thanks for some help ! By the way all my old settings are still there after reinstalling !!
Pi-hole's official installation methods comprise script-based or Docker-based approaches.
The Pi-hole team does neither develop nor endorse any apps on Asustor's App Central, nor would ASUSTOR Data Master (ADM) be on Pi-hole's list of supported operating systems.
You should consider contacting the maintainer of that app for support.