I'm not entirely sure if this is what you're looking for, but if you're using a self-hosted environment, try the following:
Open your LF Web Portal Server and navigate in your browser to something like:
http://localhost/FormsConfig/#/advanced
Once there, go to the Advanced tab and look for the setting called SecurityXFrameOptions. Set its value to: ALLOW-FROM https://YOURDOMAIN.NAME
(replace this with the actual domain where you plan to embed the form in an iframe). e.g: ALLOW-FROM https://laserfiche.com
After updating the setting, make sure to save the changes. In some cases, you may also need to restart the IIS services on the server for the changes to take effect.