If you install the app and skip the checkbox "Consent on behalf of your organization," or if anything went wrong and you need to reset the authorization and permissions, follow these steps:
Use the browser incognito mode and log in to your Azure portal.
Go to Azure Active Directory > Enterprise applications > Virto Apps.
Delete the Virto Apps.
Return to the installed Virto Calendar App on SharePoint or Teams.
Repeat the "Authorization and Permissions" steps.
Click here to read more about Virto Apps.