You can do this on the first page you see after logging into Clockwork, and it displays the active companies that you’ve connected, as well as any companies that others have shared with you.

While inside of a company, you can can navigate back to this screen and add new companies to Clockwork at any time by clicking on your profile (how you access your settings), then "Change company"

Any company you add to your Clockwork account will start on a 14-day trial by default, and you can manage the subscription for each company individually, by going into the company, accessing Settings (from the top-right dropdown menu), and signing up for the appropriate plan in Payments.

Note: if you’re on a custom/bulk pricing plan, you will be billed separately and any companies you (or your team) connect to Clockwork will be transitioned to ‘free’ accounts under your custom/bulk plan accordingly.