When a client secret is created for an app registration in Azure, It's required that an expiration is set:
 

When the expiration has been reached you need to create a new client secret in the current app registration, and update your integration connection in Vanta.

Prerequisites

• New Client Secret generated in the previously created app registration

Procedure

To update the integration, select Manage>Edit for Azure and then click "Add Subscription":

 
You can then walk through the steps to re-add the subscription that is already connected with a new client secret value:
 

 
This will overwrite the current integration, and allow you to use the new client secret.