Mass Update of Item Instance Contacts

Hi,

Each of our Item Instances has Contacts applied which are employees such as a technical contact or Cost Centre Manager.

When the employee leaves and we have a replacement, we need to complete transactions to end date or delete the existing employee contact and add a new Contact.

An employee may be applied to many Item Instances so I've been looking at the Mass Update to remove these manual transactions.

Can anyone provide assistance in how to achieve Mass update of Item Instance Contacts?

Thanks

Chris