What is the right course of action now?

When you are being overtaken on a rural road in Germany, you must make it as easy and safe as possible for the overtaking vehicle. This means you should slow down if necessary (reduce your speed) and move as far to the right as safely possible without endangering yourself or others. These actions create more space for overtaking vehicles and reduce risk, especially with oncoming traffic or cyclists nearby.

You do not need to indicate right with your blinker, as this could be misunderstood as an intention to turn or pull over. Only reduce speed and keep right. Your answers were correct: always slow down and move right, but don’t use your indicator when just making space for an overtake. This helps everyone complete the overtaking maneuver safely.