How do I pin a Workspace to a group so it appears in the sidebar?

If you have multiple workspaces setup, you can create quick links to your workspaces in the sidebar. There are 2 ways to do this:

When creating a new workspace, look for the heading 'Pin this to a group' which is currently set as 'None'. Click on 'None' and choose a workspace from the list. A small workspace icon will appear beneath the group icon in the sidebar.

Click on the Cog Icon (bottom left) followed by the blue 'Group & Apps Tab' at the top. Then select a group from the dropdown and look for the 'Workspaces' header. Click on 'Pin a workspace to this group' and a small workspace icon will appear beneath the group icon in the sidebar.
Next, click on the sidebar icon and you'll notice that the workspace is your 'new tab' one. So click on the workspaces burger menu (top-left) and choose the correct workspace for this group.