Hello,
Suppose you have created a really beautiful theme. Someone purchased that theme and now that user wants to do some kind of customizations in your theme. But this is really a bad idea to change the code in the theme itself. That's why a term introduced blank child theme.
Blank child theme as the name suggests is just a blank theme with no code written in it.
If this theme is activated on your site and some code is written in this theme then that will be applied on your site. Otherwise the parent theme code will be applied on your site(wplms in this case)
refer: http://prntscr.com/otdefl
use blank child theme then customizes the header in the child theme. this is the easiest and safest way.
if you want me to this for you then this comes under customization request. i will charge nominal cost for this customization.