$ sudo apt-get update
$ sudo apt-get install lxsession-edit 

lxsession-edit is installed in your system.

Make ensure the lxsession-edit package were installed using the commands given below,

$ sudo dpkg-query -l | grep lxsession-edit *

You will get with lxsession-edit package name, version, architecture and description in a table

lxsession-edit package basic information: