Duda has a site-wide head HTML area, so the Converly code only needs to be added once.
Step 1: Copy your install code
In Converly, click Install in the left sidebar and copy the code shown at the top. It is unique to your site. See Install Converly for the full walkthrough.
Step 2: Add it to Duda
In the Duda editor, open Site → Site Settings, then the Head HTML area (sometimes shown as Site-wide → Head). Paste your Converly code there, then save and republish the site.

Check it works
Submit a test entry through a form on your site, then open the Activity page in Converly. If the code is installed correctly, the event shows up there within a moment.
Paste your own code
Any code shown in a screenshot is only an example. Always paste the exact code from your own Install page, which contains the key that is unique to your site.