How to Enable Comments on Posts

I’m using a WordPress theme on which I don’t believe Comments on Posts are enabled.
URL is https://www.lydiatescouts.org.uk
Looking at previous posts here, I need to add <?php comments_template(); ?> into single.php, but having tried this the comment field doesn’t appear correctly. (I placed it third line up from the bottom)

Any assistance greatly appreciated.

single.php code is:
[Code moderated as per the Forum Rules. Please use the pastebin]