How to use current nginx service installed by omnibus

I have a GitLab EE instance (omnibus) running over Ubuntu 18.04.3 LTS.
I am trying to use certbot-auto to get a let’s encrypt ssl certified thoug DNS-01 challenge exclusively.
Actually I already have a let’s encrypt certified, obtained using cerbot manual. But when it comes to auto-renewal process I need to use certbot-auto and the certbot-dns-rfc2136 plugin. The thing is when I execute this command:
sudo ./certbot-auto -i nginx --server https://acme-v02.api.letsencrypt.org/directory --preferred-challenges dns -d '*.example.com' -d example.com --dns-rfc2136 --dns-rfc2136-credentials .secrets/rfc2136.ini
Nginx is not found as as path nor as a running running service.

Any clue on how can I use (or assign the PATH) the nginx instalation that is currently using gitlab?