changed theme now old one is messed up

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Like many before me, I have made the grand mistake of looking at different themes thinking I was working “privately”, hit save and the whole website changed, never to return to original state….
I figured out what the original theme was, and saved it, however, now there are jumbled bits of info all over, 2 columns, not 3, and I can’t figure out how to change the footer to say what I need to to say once more. Also, the colors I could sort of change, but I am new to this and have no idea how to recover the original site.
When I have used wordpress in the past, there were plugins and the page structure looked completely different (like boxes that I could open and add info to) also there was woocommerce and other widgets I could add and easily edit. This is a whole different beast! How do I edit this thing back to original state until I can re-do using a different host?