Please use the table_class parameter in the shortcode:
table_class="tg_table_align_top"
The complete shortcode could like like this:
[tag_groups_table table_class="tg_table_align_top"]
You will also need to purge the cache, if you use caching.
In later versions of the Tag Groups Premium plugin, the alignment to the top will happen automatically. Otherwise you need to add to the CSS:
.tg_table_align_top td { vertical-align: top; }
You can add CSS if you go to the menu Appearance -> Customize -> Additional CSS.