How do I change the synthetic voice for a section of my Action?

Trying to change the voice from female to male for one section of my Action.

I'm using the Voiceflow tool, and have uploaded my Action to Actions on Google. However, I'm not clear on how to change one section of my action from a female voice to male.

I'm looking in Dialogflow, but not seeing any place where there are tags. So maybe that's my question. Where are the speak tags in Dialogflow?

In "Fulfillment", I have the Webhook enabled, and it goes to a Voiceflow URL. However, that's just for the audio files I'm using, correct? Not the text in the tags to be spoken?

I'm wanting to have a female voice for one part of the voice app, and a male voice for the other part.

Currently, the app plays all the way through with the female voice.