After the latest version of Todoist was installed on my computer, the Todoist sidebar on my Outlook disappeared. How can I get it back?
To clarify, you installed the latest Todoist Outlook plugin, and now the Todoist sidebar is gone?
Which version of Outlook are you running? There is an Add-ins area (usually found within settings) that will allow you to enable and disable addins, please check that its there and enabled.
Also, please try closing down Outlook, clearing the cache for IE and then re-trying. If it's still not there, re-install it again.