Is there anybody who can answer this YouTube-related question?

Is there anybody who can answer this YouTube-related question?

I'm assisting a client by uploading a video for her.

How do I switch out of my account and sign into my client's business account? I signed out of my YouTube account, and then opened a tab and went to YouTube. Then I clicked on Sign in and I attempted to sign in using her business email address but I get a message saying that Google does not recognize that email address and asking if I want to create an account using that email address.  What do you suggest?