Connect to SQL database externally

I’m using the MariaDB addon and can connect to my database locally in HeidiSQL.

I also have DuckDNS set up with SSL and can connect to my main page.

However, I’m not sure how to connect to my database externally. I have port 3306 forwarded, but my with port 3306 doesn’t seem to work.

I feel like it must be something obvious. but I’m not sure what.

Take a look at this tutorial:
To open port 3306 on a public IP is probably a bad idea.

Excellent description on how to connect to an external Google Cloud SQL database: