1)

Add a workflow guide

2)

Scroll down to the Narrator settings and expand it

3)

You can select any one from the available 54 options

As soon as you click the dropdown, you will see languages and names of the voice variants for customizing the voice-over for steps

4)

Remember that you will not be able to edit this option after adding steps to this guide. When you have decided to go with an option click "Submit"

By default English language is selected with Jessa as the voice variant

5)

Notice the disabled setting when you have started with this guide