Dashing machine learning does not work. error: Package 'turtlebot3_ dqn' not found

[Fyfth]

I followed the tutorial: https://emanual.robotis.com/docs/en/platform/turtlebot3/machine_learning/#machine-learning

I input the command: ros2 launch turtlebot3_gazebo turtlebot3_dqn_stage2.launch.py
it worked as expected as it opened gazebo and I saw the correct world as displayed in the tutorial.

I opened another tab in the terminal and inputted the command: ros2 run turtlebot3_dqn dqn_gazebo 1

It resulted in the following issue.

error: Package 'turtlebot3_dqn' not found

[Yunge6666]

I have the same problem now. Have you already solved it?