You'd like to know when you last authorized the Salesforce credentials used by Heroku Connect, and re-authorize if needed.
From your Heroku Connect dashboard, go to
Settings and then
Manage Salesforce. You'll see your Salesforce username and the last time the user was authenticated.
To re-authorize, click the "Authorize Now" button on that page and the "Authorize" button on the next page. This will bring you to a Salesforce login screen where you can type the username and password. Upon successful login, your re-authorization will be complete.