Official instructions can be found here ->>

It may be need build OpenCV3 before installation. from here->>

chmod +x ros-py3.sh
./ros-py3.sh

Install OpenCV 4.3.0 here>>

chmod +x ros-py3-cv4.3.sh
./ros-py3-cv4.3.sh

Please see package name from. https://github.com/ros/rosdistro/blob/master/melodic/distribution.yaml

chmod +x add-ros-pkg.sh
./add-ros-pkg.sh ros_control

Please remove /opt/ros/melodic/bin: from PATH and make sure add follwing to ~/.bashrc

source ~/ros_catkin_ws/install_isolated/setup.bash
export PATH=$PATH:~/ros_catkin_ws/install_isolated/bin