1- Log into your cPanel account.
2- In the Domains section, click on Subdomains Icon.
3- Under the Modify a Subdomain list you can see a list of subdomains.
4- Click the Remove option under the Actions tab.
5- You will receive a warning that you are removing a subdomain.example.com. You will need to click on the Delete Subdomain button to remove your subdomain permanently.