1950 F missing

1950  50 Pfennig mint mark "F" not present but i have the coin.  how does this mint mark get added?

You may need to look here: https://en.numista.com/catalogue/pieces847.html

You're probably trying to find it on the page for the 50pf inscripted "Bank Deutscher Länder", which has only 1950G. You're coin is inscripted "Bundesrepublik Deutschland".

You are absolutely correct  Thank you.