Jetson AGX Xavier H01 Kit - ROS installation

I recently purchased the AGX Xavier H01 Kit from SEEED. It came with pre-installed JetPack OS. I am trying to install ROS Melodic, since it is Ubuntu 18.04 version. It keeps saying “E: Unable to locate package ros-melodic-desktop-full or ros-melodic-desktop”. It was suggested on the NVIDIA forum to reflash the device and try clearing out some memory, but now the device is failing to reflash using the SDK manager. Please help

“E: Unable to locate package ros-melodic-desktop-full or ros-melodic-desktop”:This situation is due to a problem with the software source, you should first use sudo apt update and then try again.
In addition, on the installation of ros system, I have made an in-depth understanding,i can share u:
1. Add ROS software source:sudo sh -c ‘. /etc/lsb-release && echo “deb $DISTRIB_CODENAME main” > /etc/apt/sources.list.d/ros-latest.list’
2.Add key:sudo apt-key adv --keyserver ‘hkp://’ --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
3. Update the software source:(i have written it up there ),if error in this step,you can try input sudo apt-key adv --keyserver --recv-keys F42ED6FBAB17C654
4. After completing the above steps, you can start to install ROS:sudo apt install ros-noetic-desktop-full
It can be installed with one click