Please follow the following steps:
1) Login to Plesk control panel.

2) Click on Subscriptions.

3) Select the corresponding Subscriptions from the list.

4) Click on Websites & Domains.

5) Click on DOWN Icon as mared in RED.
Show/Hide the list of domain-specific operations (like installing SSL certificates and apps, adjusting DNS settings, and other)

6) Click Remove Domain Alias.

7) Click Yes.

Information: The alias was removed.
