How can I import the sample data on the child theme of xstore?
also I dont see any sample data?
And when I placed the child theme on wordpress theme folder. child theme does not show on the theme options
Please, read WP documentation about child theme https://codex.wordpress.org/Child_Themes
It does not have any special options, child theme inherits all the options from the parent theme.
So, to install child theme go to Appearance > Themes > and use child theme archive to install and activate it. To install demo content go to Theme options > Import/Export > Dummy content.
1) You can use text widget and add html code with your links or you can use custom menu widget, everything depends on how it should look (Appearance > Widgets > right top bar widget area).
2) Unfortunately, there is no option to change fixed header content without additional customization.