You can check out this article to get help on how to remove an application connected to QuickBooks Online: https://community.intuit.com/articles/1145154-how-do-i-remove-or-edit-an-application-connection-to-q….
Resolution for 'application connected issue: 'How do I get rid of the Grammerly app inside of QBO!' available: Yes.
The application connected issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the application connected issue yourself by looking for a resolution described in the article. If it is a complex application connected issue or you are unable to solve the issue, you may contact us by clicking here or by using other application connected support options.
For more information about resolving issues related to application connected in Quickbooks/QBO or to get support for the issue 'How do I get rid of the Grammerly app inside of QBO!', click the link below: