According to what I have been told.
Senior U-boat officers were initially classified as militarist and were held approximately two years after the war and were interviewed to determine their political affiliation. As the Kriegsmarine discouraged political affiliation among it officer ranks very few had a Nazi affiliation. This might not have been the case for the later submarine officers who grew up under the Nazi regime. Lower ranking officers with strong Nazi affiliation were also held for a longer duration and re-educated.

The officers eventually received a release date. A date could be exchanged with another officer. They were given transportation back to Germany. They may have also received some financial help from their former Cadet Crew class members when they arrived.

There is a chapter about the release of various Kriegsmarine officers in
Eric Rust’s book NAVAL OFFICERS UNDER HITLER The Story of Crew 34