I am currently training my robot in ROS melodic turtlebot3 by following this tutorial: https://emanual.robotis.com/docs/en/platform/turtlebot3/machine_learning/ here a link to the github containg the DQN model I use for the training https://github.com/ROBOTIS-GIT/turtlebot3_machine_learning/tree/master/turtlebot3_dqn

during the training, a goal box appears in gazebo and it is the target that we want the robot to reach. during the training, the goal box gets moved to random new locations. How can I make the goal box static(stay in one location) and how can I move the static box to another location that I specify?