Remove Featured Image – Konmi Theme

If there is a theme option built in, that would be the first place to check

Another possibility would be to:

create a child theme and activate it,
https://codex.www.ads-software.com/Child_Themes

copy the file single.php from the parent theme to the child theme, and then

edit the child single.php file to comment the featured image code: on lines 22 and 58 there is code like this:

<?php the_post_thumbnail(); ?>

Both places, make it like this:

<?php // the_post_thumbnail(); ?>