Thanks for your questions. You will get all the options related to related post are under Appearance > Customize > Single Post Options > Related Post options. You will get the options there. If you want to add more features there, you need to customize the theme. You will get all the codes inside
acmethemes/hooks/related-post.php file. Please customize the theme as your need. https://doc.acmethemes.com/supermagpro/#Howtoshowrelatedpostonsinglepost?
Note: Child theme is recommend to customize theme.