Please make a copy of
EXT:xblog/Resources/Private/View/2ndContent/Templates/Main/List.html
and add your code here.
See details in @ the manual.
Look for: external manual
External Template
Sample layout with index 99
{rowOpen}{columnsOpen}{columnsClose}{rowClose}{xBlogPi1TtContentLayout}{settings_flexform_pi1_tmpl_externalTemplate}{_all}{data}
settings_flexform_pi1_list_columns: {settings_flexform_pi1_list_columns}, xBlogRegisterRecordCycle: {xBlogRegisterRecordCycle}
first in row:
last in row: