Do you know your Login-ID and Password of M&M?

If yes log in on www.lufthansa.com

Click on "My Details"--> "Miles and More"
If you have a paper-Card you will find your number there.

If you have a Plasitic-Card click on your Account statement.
There you will have your customer number.
With that number you should call M&M.

Forgotten PIN can be sent via snail mail