Hi salamu
As being said, you will need to change in layout of template, not in T4 Builder, I updated some files on your site by creating a new layout and load the blocks that I remove the 'container' class:
ROOT/templates/ja_healthcare/tpls/blocks/mainbody/fullwidth.php
ROOT/templates/ja_healthcare/tpls/blocks/mainbody-fullwidth.php
ROOT/templates/ja_healthcare/tpls/default-fullwidth.php
Then in backend of your site >> Template Styles >> I cloned the default template style of JA Healthcare to have a new one called: ja_healthcare - FullWidth to load the new layout created above and assign to contact page: