I’d suggest to try reaching out to your web hosting provider to sent you an export of DNS records. Then you can import them with a single click into the Cloudflare DNS.
Otherwise, you could look up on the DNS history online for your domain. But again, manually and individually add each of them which ins’t the case what you’d want.
May I ask if you’ve tried to delete and re-add your zone to your Cloudflare account over again?