It is not in Member Tools. You access the Send a Message feature in LCR. Log in to Leader and Clerk Resources and select the Applications tab to see it.
This link should take you there after it routes you through the login page:
https://lcr.churchofjesuschrist.org/messaging?lang=eng
Once in the tool, you can drag an attachment to the proper place on the form, or click a link to find the attachment on your computer. It should be obvious when you see the tool. Be advised that this tool was not designed for rich formatting such as in a newsletter. It only handles very basic formatting only. You will likely have better luck using very little, if any, formatting in the message body and use your attachment to provide a newsletter-type experience.
If you cannot access it, speak with your ward or branch clerk - you must be in a standard calling that grants access and you should wait about 24 hrs after the calling assignment for access to work through the church systems.