#1.
gedit ~/.local/share/applications/name.desktop

#2.Paste below text

[Desktop Entry]
Type=Application
Terminal=true
Name=unmount-mount
Icon=/path/to/icon/icon.svg
Exec=/path/to/file/mount-unmount.sh

#edit Icon= and Exec= and Name=
#Also Terminal=True/false determines whether 
#the terminal opens a window and displays output or 
#runs in the background