Footer Html edit

Hello Guys,

I am using durpal latest version 8.3.7

I am new to drupal and added newsletter block to footer region, there were already 3 block with col-sm-4 class.

Problem is newsletter block taking full width and i need to edit the html of the footer to make each block col-sm-3

I am using durpal latest version 8.3.7.

please help me out.

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/3/feed