Now run the following script:
bash /var/www/onlyoffice/Tools/letsencrypt.sh yourdomain.com subdomain1.yourdomain.com subdomain2.yourdomain.com
yourdomain.com is the address of the domain where your Enterprise Edition portal is installed, and
subdomain2.yourdomain.com (and any other subdomains separated with a space) are the subdomains for the main domain which you use.
The script will create and install the CA-signed certificate to your server and restart the NGINX service for the changes to take effect.
Now your portal should be available using the https:// address.