Unlike CSS, which a child theme will override the parent theme files, a child theme will utilize both functions.php files.
See the WordPress Codex: https://codex.wordpress.org/Child_Themes#Using_functions.php
And the Buddypress Codex: https://codex.buddypress.org/legacy/building-a-buddypress-child-theme/
So don’t copy it over. The functions are being applied in your child theme already. If there are additional functions you want to add in your child theme, add them to the child theme functions.php file.
