How do I delete specific emails from under the email tab in a contact?

Outlook is synched to Bigin and the emails we want to delete from the Bigin contacts have now been deleted from the outlook inbox.

The reason we want to do this is because we had quite a lot of these emails, all with the same subject title, that are not relevant to Bigin contacts. It makes it more difficult to spot relevant emails under some of our contacts email history, when they are full of these irrelevant emails.