The placeholder file name “Cloudflare.crt” is meant to be replaced with “origin-pull-ca.pem”. That is if you uploaded the file without changing it’s name.
The placeholder file path “/etc/nginx/certs/Cloudflare.crt” is meant to be replaced with the location that you decided to upload/keep your origin-pull-ca.pem certificate.
Change the above lines in your nginx configuration to where you uploaded your origin-pull-ca.pem. For example (and this will only work if /etc/nginx/certs/ is an actual directory that you use):