$ sudo apt-get update
$ sudo apt-get install libgdm1 

libgdm1 is installed in your system.

Make ensure the libgdm1 package were installed using the commands given below,

$ sudo dpkg-query -l | grep libgdm1 *

You will get with libgdm1 package name, version, architecture and description in a table

libgdm1 package basic information: