What is the right course of action in this situation?

In this situation, the correct action is to slow down. When your lane is ending or merging into another lane, German traffic rules require you to adjust your speed so you can safely merge and yield to oncoming traffic if necessary. Slowing down gives you more time to watch for vehicles in the lane you're merging into and ensures a smooth and safe transition. Accelerating or continuing at the same speed could make merging dangerous if there are vehicles alongside or ahead of you in the remaining lane. Always be prepared to adjust your speed and watch your surroundings when lanes merge.