Hello, @kdpisda

You’ll need to first remove the domain’s certificate and then to remove the domain name. You can navigate to your account –> Settings –> Security –> And then delete the Certificate for the domain name in question

Once this is done you can delete the domain name.
To delete a domain, log in to the control panel and click Networking in the main menu to go to the Domains tab.

Open the More menu of the domain you want to delete, then click Delete. In the confirmation window, click Delete Domain to permanently delete the domain and its records from the account.

You can find more information here: https://www.digitalocean.com/docs/networking/dns/how-to/delete-domains/

Hope this helps!

Regards,
Alex