Where to add a filter in a themes functions.php?

Hi.

I need to add this filter to my themes functions.php file:

add_filter( ‘wp_tiles_load_more_text’, function( $ret ) {
$ret = ‘Get more posts!’;
return $ret;
} );

I tried adding the lines in the file = totally haywire.

Could a kind soul please tell me exactly where I should add these lines in the functions.php file please.
Maybe you could demonstrate by adding the lines in a functions.php file and paste it here.

Thank you all!
BR LSJ.