Switch to another firm or client

At the top of the left menu click the card that shows the firm name and, below it, the client name (on a phone it is the name at the top of the screen).
Under Switch firm pick the firm. You land on that firm's list of clients.
Under Switch client pick the company whose books you want to open. This list appears once a firm is open.
With many clients a search field Search clients appears. Clients you opened lately are listed under Recent.
To add one, click New client (only if your role may create clients) or New firm.
The name in the card always shows whose books you are in. Check it before you book or send anything.