Navigate to https://secure.myob.com/
Under the Authorisation heading, you will have a list of apps that you have authorized in MYOB. Click the Revoke Access button beside the app name, Crunchafi Data Extraction (US/AU/EU Edition)
Note: You may only have Crunchafi Data Extraction (US Edition), Crunchafi Data Extraction (AU Edition), or Crunchafi Data Extraction (EU Edition), so you will typically only have to revoke access to the connection specific to your region.