Here is the link to the updated CRM Online Outlook Client diagnostic wizard. The wizard has been updated to include recently discovered issues.
The older troubleshooting wizard for both online and onpremise was here https://support.microsoft.com/en-us/gwt/10070 But it hasn’t been updated in a while. So if you are using CRM Online be sure to use the updated wizard link above.
Also take note that starting with the CRM 2015 Outlook Client, a dynamic help feature was added. Now depending on the error you receive you will be directed to a KB article for that specific error rather than a generic help page. The new CRM app for Outlook also includes that feature.
Read more about it here: