To switch accounts, simply select the name at the top of the screen, and choose the name of the person you'd like to switch to on the screen that appears.
If the name you are looking for does not appear on the screen that appears, it may be because the person you are supporting has not accepted your invitation to support, yet.
Consider sending them a reminder by going into settings->Circle of Care, and selecting the envelope icon to the right of their email address. This will resend your invitation :)