Facebook plugin "experiment" and I trashed my home page

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New user to 5.7 so please bare with anything stupid on my side.
So was happily playing around with 5.7 and a few themes and thought I would toy with facebook integration.

I rashly dropped the following code into a block:
<div id="fb-root"></div>
<script>(function(d, s, id) {
var js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id)) return;
js = d.createElement(s); js.id = id;
js.src = "//connect.facebook.net/en_US/sdk.js#xfbml=1&version=v2.6&appId=148155058646411";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>

It has totally trashed my layout, should be no problem let me restore a previous version. Well I can see changes to the page but the layout remains a mess. I cannot edit the block to remove the above code, I cannot roll back as the effects of the code remain present even on versions that never had it.
If I change themes and layouts, the block is not visible to be edited.
Is there a way to get at the home page in Cpanel? So I can delete the code?
I can see the offending code in source, just no idea how to get at it ;)
Super weird that all my versions are being affected.
Failing all of that how does one make a new home page in 5.7
Thanks

 
slowdive replied on at Permalink Reply
"crisis" averted somehow I must have deleted the offending block.
I just started randomly deleting everything in the header and seems I got it eventually. That or it was a weird caching issue, as i cleared cache to no avail. However when I went to look at the system information to post a support request with theme developer and came back, it was fine. Seemingly having rolled back to the version I selected.

So I suppose this can be considered closed, however if or when someone has the time to link or explain how one would edit the source code of a page or block, I remain curious.
Thanks