Hello,
please create a freshdesk app (see screenshot) which allows to send messages based on selected option:
Option 1 - Freshchat Whatsapp:
Send a message with the Freshchat outbound api see doc here [login to view URL]
Option 2 - Twilio SMS
Send a sms message with the twilio api
# UPDATE:
You can probably use sample apps from freshworks to do this.
[login to view URL]
This sample app creates already a widget in the sidebar: [login to view URL]
# UPDATE 2:
To add widget in the sidebar you can use the following doc
[login to view URL]