I have problem with WordpPress 5.3.2. My theme is Glob (free version). I have tried everything but nothing is happening. I have the error only in admin but it make me very stressed. I want your help.

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'my_custom_excerpt_length' not found or invalid function name in .../wp-includes/class-wp-hook.php on line 288

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'my_custom_excerpt_more' not found or invalid function name in .../wp-includes/class-wp-hook.php on line 288