First, ensure that you are signed in as an admin. If you don't see any option to send a text, you may not be an admin on the account.
Next, check that you are using the latest version of the app. To check which version you are running, open the app and go to Settings > About Grasshopper and check the version type.
Finally, if you still do not see texting, you may not have added the feature yet. You can that online, but not directly within the app.
To enable texting, log into your account on www.grasshopper.com and select Settings then Features to see if Grasshopper SMS is enabled. If you have more than one Grasshopper number, you can see which numbers do have SMS enabled here as well.