I deleted my domain from cloudflare which removed the DNS records from the platform. I went to my registrar and they say I need to change my DNS records here as they are still pointing here. I cannot do tat as the domain is deleted and I cannot access them.
What feature, service or problem is this related to?
If you want to remove Cloudflare completely then change those nameservers to those for your new DNS provider.
If you want to use Cloudflare again, just add your site back to Cloudflare as you did when you first added it. Note that you will get allocated a new pair of Cloudflare nameservers so you will need to set those at your domain registrar.