How to eddit child theme

Yes I googled and searched this for like an hour already and still can’t figure it out.

I want to edit this line:

<button value=”1″ class=”_42ft _4jy0 _5gyi _ew1 _4jy3 _517h _51sy” type=”submit” style=”
“><i class=”_3-8_ img sp_iGQuBtwYdd4 sx_09ea7e”></i>Share</button>

I want to add:
margin-right: 38px;

to my child theme so it has this in it like this:
<button value=”1″ class=”_42ft _4jy0 _5gyi _ew1 _4jy3 _517h _51sy” type=”submit” style=”
margin-right: 38px;
“><i class=”_3-8_ img sp_iGQuBtwYdd4 sx_09ea7e”></i>Share</button>

But when I add this to my Child theme nothing happens :/

am I doing somthing wrong?

Do I have to change the code or something

any help is appreciated.

I can’t find any basic instructions of copying and pasting from inspector to child theme on line.

yay learning.

what do I type in my child theme to do this?
Thanks