Connect to Server with a Different User Name (Yosemite)

I'm on 10.14 and a user is trying to connect from 10.10 (Yosemite). They logged in once some time ago using a different account, and now they can only connect with that account. There doesn't appear to be any way for them to force the user/password dialog to appear.

On my machine, there is a "Connect As..." button in the Finder window of shared volumes, but there is no such button in 10.10. How can this user log out and connect to my Mac (using AFP) using a different account?