navwalker.php child theme location

Have not found this answer yet by searching.

I have altered the navwalker.php and it does what I want it to do, but I know i need it in the child theme so it doesn’t go back to default when the theme is updated.

I moved it over to the child theme director, but not sure where to put it as I created and inc directory and put it there, and it doesn’t work, and have it in the main director and it doesn’t work.

I know it doesn’t work because i put the original navwalker.php back to normal.

when creating child files of themes, does the directory hierarchy have to stay the same?

or are certain files not able to make a child of, i know functions is a no.