The appearance of the chat bubble can be changed in several ways. You can change the welcome message that is initially sent, the title of the bot, its colour, and which questions are suggested upon opening the chat bubble.
Simply:
Login to your account.
Navigate to the bot you want to modify.
Select the Destination you want to customize the appearance of.
Head to the general tab and adjust the title, welcome message, and colour of the bot.
You can choose to provide specific suggested questions, but if not, then they will be automatically generated for you.