Change a function in child theme

I made a child theme from Zerif Lite and I would like to change a certain function from the functions.php. More specifically I want to change the way the “read more” is shown.

In the original functions.php it is coded in the following part:`
function zerif_excerpt_more( $more ) {
return ‘<a href=”‘.get_permalink().'”>[…]</a>’;`

I would like to permanently override the brackets and dots with my own text. I have tried some options but all I get is a massive 500 error on all pages.

Could anyone help me creating a working functions.php for the child?