Menu disappeared after update

After the last update my mainmenu disappeared! I could bring it back by setting back yesterday's backup. The mainmenuy is located in header-right. As far as I understand it is build through "inc/custom-header.php". My idea is to move that file to the child-theme directory, but do I need to make an adjustment elsewhere to force the system to use the childtheme's inc/custom-header.php instead of the theme's inc/custom-header.php? If so: in which file?