Go is the label text of submit button and not part of voice command in both HEF and non-HEF mode. In both case, proper training examples should be added.
For hands free mode on mobile, should be triggered by "hi Bixby" and not touch screen any time during the conversation. "hi, Bixby" --> "ask my capsule to do input prompt" --> Bixby respond "Enter Quantity" and opens mic waiting for input --> "five" --> continue the flow as 5 is taken as input.
For normal non-HEF mode, hold button and "ask my capsule to do input prompt" --> Bixby respond "Enter Quantity" --> user can either type 5 and tap Go or hold button again and say "5" then release the button --> continue the flow as 5 is taken as input.
Customized input in HEF and non-HEF can be supported with proper training examples, developer can support utterance like "go ahead with 5" or "quantity is 5" or "I want 5". It is possible to training "go" with a default value to the input prompt, however, it is not possible to fill the form by entering text, and training "go" utterance to take the input value.
The training example should be marked as "at prompt for [input type]", please read more in https://bixbydevelopers.com/dev/docs/dev-guide/developers/training.training-for-nl