Child theme troubles

Recently I had some trouble with my website (also see https://kriesi.at/support/topic/all-styling-gone/)
Now I have pretty much everything back in order. But I’m not using my child. I had to quickly edit functions.php to get some stuff working again. And manually reset all styling and widgets. And all of the css is in the quick css.

Now I would really like to go back to a child theme. My old one is still not functioning correctly. So I can’t switch to that one.

I made a new child theme but can I somehow switch to the child without losing everything again. When I preview the child theme I see that widgets/menu’s are gone again.

thanks