The only way that you can move "Leave a comment" from above the posts to the footer of the posts, is to make some coding changes to a couple of theme template files from the WordPress Themes Editor. If you feel comfortable enough to follow these steps, try giving it a shot, but first take a backup of the files that the changes will be made to (see Step 1 below):
1. From your hosting control panel file manager, take a backup of the following theme template files (just in case something goes wrong in the steps that follow): wp-content/themes/vortex/content.php and wp-content/themes/vortex/content-single.php.
2. Create a child theme. See the following: Child Themes
3. From the WordPress Dashboard, go to Appearance -> Editor
4. Next, from the template file list on the right hand side of the theme editor, select the template file called content-single.php
5. Look for the following lines of code within the top section div class="entry-meta":
<?php echo vortex_post_date() . vortex_post_comments() . vortex_post_author() . vortex_post_sticky() . vortex_post_edit_link(); ?>
6. From the above lines of code, find and then move the following line enclosed in quotes "vortex_post_comments() ." to the bottom section of code within div class="entry-meta-bottom". It should end up looking something like this:
<?php echo vortex_post_category() . vortex_post_comments() . vortex_post_tags(); ?>
</div><!-- .entry-meta -->
7. Click Update File to save the changes
8. Repeat steps 4 through 7 for the template file content.php.
If something goes wrong as you make the above changes, you can reupload the backups that you created, overwriting the modified files.