Hi
In this case, you will need to edit LESS file:
[your_site_root]/templates/ja_morgan/less/variables.less
Look for this line of code:
@grid-float-breakpoint: @screen-md-min;
and change to:
@grid-float-breakpoint: 1024px;
the screen size smaller than 1024px will display menu button.
Remember to backup your site first and compile less to css: https://www.t3-framework.org/documentation/bs3-configuration#compile-less