Bad JS customizations - how to fix in the backend?

Hi,

Currently using v1.3.0.beta3 +13. We’ve attempted some javascript header/footer customizations via:

Customize -> CSS/HTML -> head and body

but we’ve ended up ‘breaking’ discourse due to our JS containing errors. This in turn means we can’t edit, delete or enable any other saved customizations. Basically, we can’t edit or remove our own javascript:)

How can I remove these changes in the backend? Is there anything else I can try?

Thanks.