PHP - Moved: Onmouseout/over Working On One Site, But Not The Other...

The Wordpress Atahualpa theme does not appear to be compatible with php 7.2. I know very little about php. I get the following error message in my error log:
=====
[24-Jan-2019 22:14:03 UTC] PHP Warning: Declaration of Walker_Comment2::end_el(&$output, $comment, $depth, $args) should be compatible with Walker::end_el(&$output, $object, $depth = 0, $args = Array) in /home/armst5/public_html/MyBlog/wp-content/themes/atahualpa.3.2/atahualpa/functions/bfa_comment_walker.php on line 145
=======
What does this mean and can I fix it?