Nextcloud doesn't start because I updated the container one version above (25 to 27)

Hello! I know that this question has been asked many times, but I just want one thing clarified: everybody mentioned about manipulating the version.php file from /var/www/html, but if I look with WinSCP on my NAS (openmediavault), /var/www/html only has a file named index.nginx-debian.html. My guess is that this path is more of a virtual one, docker-related. So how can I access /var/www/html and modify the file? Thanks!