Cannot see the API button to set variables while creating a template

I am trying to follow the "Replace image in template" (https://docs.heygen.com/docs/replace-image-in-template) API docs but I cannot find the API button in the UI to set the variable name for the image.

I am using the free plan but the API pricing page (https://www.heygen.com/api-pricing) says that "create video from template" is a feature available in the free API plan as well.

What do I need to do? Can you please advise?