$ sudo apt-get update
$ sudo apt-get install erlang-reltool 

erlang-reltool is installed in your system.

Make ensure the erlang-reltool package were installed using the commands given below,

$ sudo dpkg-query -l | grep erlang-reltool *

You will get with erlang-reltool package name, version, architecture and description in a table

erlang-reltool package basic information: