When you active the child theme, all your settings and custom CSS will be lost, because they are only belong to parent theme, you need to reset all settings include LOGO.
For the custom LOGO didn’t work in child theme, I guess maybe it’s a small bug in parent theme that I will improve, or you can leave me your wp login information with private reply, I can make it work soon.
Or you can directly replace the default LOGO image file to yours in “img” folder of child theme.
For how to customize the child theme, it’s a customization issue that not include in the support, there are many articles on google tell users how to customize the theme with child theme, however, I can help you to fix the LOGO issue soon.
Thanks!