Step 1:

Go to the folder from the main menu.

Step 2:

Click the publish link at the bottom of every checklist you see.

Step 3:
Go to the 'YOUR OWN LANDING PAGE' from the left side menu.
Copy your Checklist's VALUE & JS code.
In this example, I am using  WordPress 'Elementor' Landing Page Builder. The concept is simple and almost the same in all landing page builders or even if you are using your custom HTML.
PASTE the copied VALUE inside any anchor tag (link or button) to trigger the Opt-In form.
PASTE the JS code as well after the anchor tag (link or button) element. (see the video below)

Now you will be able to see your opt-in form by clicking the anchor/button.