It was my mistake that I had used the BSP package for Jetson Nano that has Jetpack 4.6.2. but the Jetbot image needs Jetpack 4.5 and lower versions. So the procedure remains the same except get BSP packages from here https://developer.nvidia.com/embedded/linux-tegra-r325
Once the Jetbot Image is overridden on the Jetpack image using the Etcher tool, the SD card is ready to boot.
Initially, what I observed was that the display screen gets ON but remains black, but the background image is booted successfully. I could access the device through serial communication and assigned it Wifi and IP. I could see the assigned IP on the display of the Jetbot. I could access the Jupyter-lab through the assigned IP at port 8888 with the password jetbot.
Then I realized the GUI was disabled, Which I enabled by entering the following command and rebooting the device.
sudo systemctl set-default graphical.target
Now Jetbot works fine. Thanks.