I was getting notification that the environment has chanmged from ROS kinetic to ROS noetic, and was shown commands to set it for noteic but as soon as I removed files & did catkin_make, It gives "Comand not found" error.
The screenshot indicates that there’s an error in your ~/.bashrc file, on line 3 of the file. This suggests that you modified this file at some point and introduced that error.
Now, we need to fix that error. Is it something you can fix? Otherwise, we’ll need to jump in and fix it for you.