$ sudo apt-get update
$ sudo apt-get install partman-ext3 

partman-ext3 is installed in your system.

Make ensure the partman-ext3 package were installed using the commands given below,

$ sudo dpkg-query -l | grep partman-ext3 *

You will get with partman-ext3 package name, version, architecture and description in a table

partman-ext3 package basic information: