If you wish to turn off your bot's Welcome message, you can easily do it by going to Settings>Welcome message where you should check the "Disable Welcome message" option:
Why would I want to turn off the welcome message?
The welcome message is very helpful for new customers but there are a couple cases where it might interfere with other things you're doing. We recommend turning off the welcome message if:
1) You are using another bot as your primary bot on the Facebook page and adding Octane AI as a secondary bot.
2) You have a customer service team who replies to all Facebook messages manually.