Adding Trusted Domain

I downloaded the latest virtualbox appliance and installed. All is good there.
I need to add a trusted domain, but for whatever reason I cannot seem to run as sudo and also I am denied access to /var/www/nextcloud. Has this always been the case? I dont remember this being locked down.

Can someone please run me through the steps to get to the area where I can access the config.php file. Once there I will be fine, but I’m having a brain fart to get to that area.

Thank you guys.