Thanks for your post, and welcome to the community! If you're using Workspace, you should be able to use the search box in the upper right hand side to search for the sender's name or email address. After the search completes, you should be able to use the Select All checkbox and select the messages on the page and delete them.
If you're using another option, like Office 365, please feel free to give more info or follow up. If other users have tips or tricks for quick mailbox maintenance, please feel free to chime in!