Whether you can do your own hair and makeup is completely up to you. If you’re comfortable doing self-styling, feel free to say so — and if not, it’s perfectly fine to politely decline.
Note that if you agree to self-styling, clients may expect a certain level of quality. It's helpful to request a reference image or brief from the client in advance. If additional styling prep is required, you may also choose to reflect that in your rate. All details should be discussed before signing the contract via the chat system.