You are planning a migration of your Salesforce organization to another geographic region (e.g., AP to EU, NA to AP, EU to NA, etc.) and your Heroku app, Heroku PostgreSQL add-on, and Heroku Connect add-on are still in a region that's geographically closer to your old organization region.
It's likely that you may see worse synchronization performance than you did previously after your Salesforce migration. This is because Connect talks to your organization via the Salesforce API and will continue to work from the region you created the add-on in. The additional distance will create overhead for establishing connections, retrieving data from Salesforce, and sending data to Salesforce.
If these consequences are unacceptable and your application's location does not matter, you may consider recreating your space, app, database, and connection in the new region. If you'd like to do this without first destroying your old Heroku space, app, database, and connection you must use a new Salesforce integration user to prevent issues with synchronization while performing your own migration.