Go to your page (https://www.qrz.com/db/ON8WI), click "Edit" in the upper right corner of the menu and click then "Edit ON8WI". Find the section labeled "Add a special callsign such as ON8WI/MM, ON8WI/P34, etc." Choose "Non-DX modifier (such as /R /M /P /QRP, etc)" Put the "M" in the blank spot after your callsign below. Hit "Continue" and you should be good to go.
Thank you for your reply. De /M is added but it doesn't pop-up in my main Page de ON8WI See pic below