I have tried unsuccessfully to update the CNAME records with Domain Registrar (LCN.com) but I’m not sure if I am putting the information in the correct cells as the titles for the records are different:
For starters, you should see the blue banner there. It says you’re using our nameservers and so need to set the CNAME records through our control panel. With a link to find instructions.
Nothing you configure on your registrar’s nameservers will change anything because you’re not using their nameservers.