OwnCloud need help changing the listening port!

How do I go about removing the cert and if I do that then i’ll nolomnger be able to access Owncloud VIA Https correct?

Below screenshot are examples, when I turnj of port forwating for 443 for ownclound I can get to Porkbun where my domain is hosted VIA NGINX proxy - Still ahven’t gotten an SSL cert worked out.

If I reeanable that port for Owncloud i can access it via https but with it enable if I try accessing NGINX i get the below certificate error and a plceholder page.