How to set a field of the form component (configured using form controller) with a variable in UIB

[AaliyahBeg]

In reference to the documentation (https://docs.servicenow.com/bundle/washingtondc-api-reference/page/app-store/dev_portal/API_referenc...), how can 

api.data.<data_resource_id>.setValue(Object payload)

be used  to set a field of the form component (configured using form controller) with a variable present in a client script. Tried using this syntax, it didn't work.

Thanks