At this step was my mistake
To set the environment variables permanently, edit .bashrc in your home directory.
Use your favourite text editor to edit .bashrc, for example gedit:
$ gedit ~/.bashrc
Add the following line at the end of the file, then save it:
export PATH=$PATH:$HOME/omnetpp-5.0/bin
You need to close and re-open the terminal for the changes to take effect.
try using nano instead of gedit
#nano .bashrc
and notice the difference in the line
export PATH=$PATH:home/amr/omnetpp-5.0/bin
only 1 $ sign and also choose the correct root to /bin
I hope this will help