Duckdns wildcard + how to set the root location to use www.subdomain.duckdns.org

Running SWAG & DuckDNS; using DNS validation and a wildcard. All good, aside from the stated limitation that the main URL isn’t covered under SSL.

Container startup includes the following comment:

the resulting certificate will only cover the subdomains due to a limitation of duckdns, so it is advised to set the root location to use www.subdomain.duckdns.org

How would I go about setting the root location to the www sub-subdomain, as it suggests (ideally in a way that main url redirects to www sub-subdomain, avoiding certificate warnings)?

Any advice would be appreciated!