Unable To Change Salesforce Connector User to B2BMA Integration User in Account Engagement Standalone Application

The only way in which you can switch from a custom Salesforce Connector User to the default B2BMA Integration User is via the Account Engagement Lighting App. It cannot be done from directly within the Account Engagement standalone application. So firstly, you'd need to make sure that in order to do this change, your user has access to the Account Engagement Lightning App which can be done by following the steps in this article. 

For any user with the ability to access the Account Engagement Lightning App looking to make this change, the first step would be to retrieve the exact username of the B2BMA Integration User in your Salesforce Org. This can be done by navigating in Salesforce Admin Setup to the B2BMA Integration User record in Salesforce. Once done, make a copy of the B2BMA Integration User's username. Then, follow these steps from within the Account Engagement Lightning App with a user that has the Account Engagement User role of Administrator:

1. Go to the 'Account Engagement Settings' tab within the Account Engagement Lightning App
2. Then, go to the 'Connectors' section
3. For the Salesforce Connector, please select the 'Edit Settings' option for this connector
4. In the 'Change Trusted Connection User' section, remove the existing custom Salesforce connector username and replace it with the full username of your B2BMA Integration User which was retrieved earlier via the initial step noted above
5. Select the 'Change Trusted Connection User'

As logging in as the new intended connector user is not required in the Account Engagement Lightning App, when doing the above steps, after it has finished processing, a message of 'Your Salesforce Connector User is verified' should display with the Salesforce connector user changing to the B2BMA Integration User.

Note - If you are using a Salesforce Connector Version 2 but encounter an error when attempting to change to the B2BMA Integration User from within the Account Engagement Lightning App, you would have to ensure the B2BMA Integration User profile in Salesforce is assigned to the connected app 'Pardot_to_SF_Integration_Secure_Connected_App'. See this article for more.