Alsace family name change from Marshall to Schmitz

We do plan to visit Alsace in the near futire. I will definitely contact you for resources.

We have a family member that was a translator and he lived in the Alsace region during the war between Germany and France. He ended up changing his name from Marshall to Schmitz and left to come to the US. We believe based on what were told that he probably did it to get away from the war.

I am not sure if he is the one who changed his name or if it was his father. Do you have any recommendations for me to try and research this?
The Schmitz that came from Germany was Michel (Michael) Schmitz born October 13, 1820 in Luxembourg, Germany born to Michel Schmitz and Barbara Mary Dietz. Michel Schmitz was born in France. His parents were born in France. They immigrated to the US 1850.
Barbara Mary Dietz was born in December 4, 1834 in Prussia, Germany. Her parents names were: Father: Anton Gottschalk Mother: Dorothea Deitz
moved to Michigan on or before 1880.

I was also wondering if you could please give me any recommendations where I can find and purchase the birth certificates and their marriage license?

Thank you for your time,
Terese Marschner