You can switch between the companies you are currently a member of by clicking on the profile icon on the bottom-left menu.
Next, you can select your company/name and a dropdown menu will appear with the companies that you are a member of:
You have the option to toggle back and forth between the company workspaces that you're a part of:
Note: At this time, each Bonsai account can only host one company that you own. If you are invited to join another company as a team member, you will be able to switch between your own company and the invited company in this section.