To add Yoxel tabs to the Salesforce toolbar proceed by clicking “All tabs” button (plus sign on the right side of the main navigation panel) and then clicking "Customize My Tabs" button:

Once you are on the Customize My Tabs page, (1) in the Available Tabs section scroll to the Conversations and Yoxel Sync tabs, click on them and (2) add them individually to the Salesforce toolbar by clicking the Add arrow. You are also able to (3) prioritize the tabs by moving them up or down with respective buttons. (4) Click the "Save" button after you are done.