KG 53 Pilot Vollmer

Hi, I am not sure what kind of info everyone here has, but I am searching for any available information about KG53, and where I could find more information about my grandfather's service with them. My grandfather was named Erich Martin Vollmer and he was first a flak gunner and then a pilot of He-111 and Ju-88 bombers in Kampfgeschwader 53 Legion Condor in WWII. I am interested especially in when/where they surrendered to the Americans and what happened to the members of KG 53 at that time. The story is kinda murky, but all I know is that my grandfather surrendered to the Americans at some point and was a prisoner for a while and made his way (I think he walked?) back to his hometown in East Germany in December 1946. I think he was an officer by the end of the war but I am really unsure about that. I'm curious about his activities during the war and after, and why and under what circumstances he was released.