From the homepage of the toolkit, navigate to the Text tab.
In the Text tab, make sure two key steps are completed first:
Enable SMS responses for this survey.
Select a public number for this survey.
Once you've set those up, you can create inbound Keywords in the keyword table:
Choosing a segment and language are optional. If you select a language, messages will be automatically translated by Google Translate, but you may customize the prompts and options in the Settings tab using last-mile translation.
Note: if you pick a keyword that is already being used by a different survey, you will receive an error message stating "is already in use" and you'll need to pick a different keyword.
Your keywords that trigger the survey will appear above the keyword table. You can delete a keyword by clicking the red trash icon.
See also:
Create segments for SMS keywords
How to add a text keyword to a meeting