Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
I am afraid I don't understand your ask/requirement here.
- Have you already delegated your domain to Azure?
- If so, do you mean to say there are DNS records not in DNS Zone but still available while doing DNS queries.
- If so, make sure only Azure NameServers are used in your domain registrar's NS records and nothing else.
- Or you created the Zone in Azure but you are yet to delegate the domain?
- If so, you just have to update the NS records in domain registrar's page
- See : Retrieve name servers and Delegate the domain
Wrt, "Is it possible to remove the old record completely?"
- If you are the owner/manage the domain, you should be able to delete those records
Cheers,
Kapil