If you’d like to use a plugin to do this work, then the WP Bulk Delete Plugin should do the trick for you.

•  First, go to your Post section in the Admin area of your backend.

The Bulk Delete plugin lets you choose to delete comment based on a number of different options. For example, you can delete comment based on

• Basic Filter
• Comment Type
• Author Filter
• Comment Meta Filter
• Post Filter
• Date Filter
• Action

Basic Filter

Comment Status :- Select the comment statuses that you want to delete.

Comment Type

Comment Type :- Use this filter to delete comments based on their type. Simply select the comment type you want to delete.

Author Filter

Comment Author :- Select the comment author whose comments you want to delete.

Comment Author Email :- You can delete multiple comments at once by separating the authors’ email addresses with commas.

Comment Meta Filter

Comment Meta Key Settings :- Use this filter to delete comments based on custom meta values. Enter the meta key and the value you want to match. Choose the appropriate comparison type from the dropdown to specify how the value should be compared.

Post Filter

Comment Posts :- Select a post whose comments you want to delete.

Date Filter

Comment Date :- You can delete comments between the start date and to end date.

Comment Date :- This option will work well with Scheduled Delete, which will help to delete comments of the selected option from the scheduled run date.

Action

Limit:- Set the limit over post delete. It will delete only the first limit posts. For example, if you write a limit of 2 you delete a maximum of 2 posts/pages.

Detele Time:- WP Bulk Delete Pro provides functionality to schedule deleting at a particular time. and You can choose the scheduled at option at Delete Time to schedule delete. it has 2 options.

Delete now => It will start the delete operation just after you press the delete button.

Schedule Delete => If you want to run the delete operation later at a particular time. You can also repeat delete operations Once Hourly, Once a Month, once weekly, Twice Daily, Once Daily. You can see repetitive scheduled deletes at the WP Bulk Delete>Schedule Delete page