Issues - please help

I accidently started drawing on 'background' layer in photoshop (I usually make a second layer), during which I was able to erase lines without erasing the white background, but I accidently changed it to 'layer 0' and when I erased my lines, I would erase the white background as well.

Is there a way to change the layer 0 back to 'backgrund layer' or somehow take the lines I drew and move them to another layer?

help would be appreciated, thanks