Magent 1 domain name change causes COrS errors and site breaks

I have two magento 1 sites on separate servers: this is undoubtedly the wrong way to do it and I am still on a learning curve (steep) with changing themes in M1

https://www.petrolthreads.co.uk (old site) (M1 1.9.2.1 php5.6)
https://www.petrolmugs.com (development / new site M1 192.4.2 php7.2)

Both work well: the old site is slow and, well, old and the new site is ready to replace the previous site, so this is what I have done:

  1. changed the domain of the whm / cpanel account for petrolmugs to petrolthreads.co.uk

  2. edited the base URLs in the cor_config_data table to be http://www.petrolthreads.co.uk/ and https://www.petrolthreads.co.uk/ so that they are not safe and secure respectively.

  3. pointed the dns petrolthreads.co.uk to the new server.

I can navigate to the new site through petrolthreads.co.uk but the site does not work: it has many CORS errors (for sources) and 404 not found (for the slider) and the currency exchange stops working.

I have no idea where to look and any suggestions / help would be appreciated. The images show the problems: I have undone my actions and the sites have worked again now.

CORS and 404 errors

the slider does not load