The following article describes how to install the report Phishing addon for Google Workspace.
When a Phishing Campaign is underway and users start receiving phishing emails, they have several choices: they can either open, inspect, and ignore the email, click a link, provide their credentials, and fall for the phishing attempt, or report the suspicious email.
Report Phishing Extension is a special button that appears on the email message taskbar in the right top corner. This allows users to easily report suspicious emails and helps organizations assess the effectiveness of their anti-phishing training. It also provides valuable feedback on areas where additional training may be needed.
In order to proceed with getting the extension, please navigate to the phishing menu in your admin console, and press on the "Extensions" menu: 
Insert the email address to which the reported emails will be forwarded into the "Report To Email" field & press save afterward:
We recommend creating a direct email (or group), for that. Example: incident-response-team@yourdomain.com, reportedemail@yourdomain.com, etc.
Once the email is saved, you can use the manual according to the platform you are on.
Installing the extension(the app can be installed by admins only):
As an Admin, please navigate to the dedicated app page in Google Workspace Marketplace
Once there press on Admin install:
Proceed with the Admin install: 
Once done, select the desired group(s) to which you would like to install the app, or select to install it for everyone.
Moving forward, you will see the following screen:
Once the above steps are done, you should be all set.