In your QuickBooks Online (QBO) company, click the My Integrations icon, then click Manage integrations. see screen shot
Click the Disconnect button. see screen shot
Alternative method: You can also disconnect the integration directly from the Utility App. see screen shot
When you disconnect, the following confirmation is prompted, and you will receive a confirmation email from Intuit. see screen shot

To reconnect, click Connect to QuickBooks to link the ExcelFSM QuickBooks Online Utility App back to your QBO company.
Alternative method: Repeat Step 1
Once reconnected, create the ExcelFSM QuickBooks Online Company File as described in Step 2