To use any child theme out there all you need to do is upload it like you would with any theme then activate.
I built my website before you offered the child theme.
Child themeing isn’t a new concept or even unique to my themes. They’ve been in use long before I’ve submitted a theme to wordpress.org. If a user finds it really necessary to use a child theme then they should really be the one to create it. I just offered a ready-made one to make it convenient.
How does this effect all the settings I have already created on the parent theme?
The settings on the theme options page will remain the same. If you’re talking about changes/edits you made on the actual theme files then no, you’ll have to do them again on the child theme.