What is the right thing to do in this situation?

In German traffic rules, when you see a lane closure sign or a lane control signal indicating that your current lane will be closed ahead (such as a red "X" over that lane), you must leave that lane as soon as it is safe to do so. This often means ceasing an overtaking maneuver and moving into the open lane. Continuing to overtake or maintain speed in the closing lane is not allowed, as it may create dangerous situations or traffic jams. The key rule is to follow lane control signals promptly and safely to maintain orderly traffic flow and enhance safety on highways. So, stopping the overtaking and moving into the right lane when that lane is open is the correct and required action.