in a child theme, how to change capacity required by to access specific admin page

I use a theme which adds a menu with different menus in WP admin.
Looking into functions.php pf the theme, I see that the menu requires "switch_themes" capacity, while submenus only requires "manage_options".
I need to have users access this menu but not switch themes.
So I need to change the capacity required for the menu from "switch_themes" into "manage_options".
I have done it in the theme file and it works.
But to do things the right way, I would like to do it in a child theme.
How to proceed?