Playground issues calling function

i wonder how to do a “message” or “prompt” to user from assistant…
something like assistance says “Hi, i am assistant responsible to providing red light camera information”, so user will see this message and be able to ask better questions…
initially i thought that i can do it using instructions, but looks like instructions are to tell assistant how to process information…
i tried to use message, but assistant take only “user” role…
any help would be appreciated

Thank you
YK