Go to your Google Security Page.

Click on "Apps with account access" in the left-hand sidebar.

Click on "MANAGE APPS" in the "Apps with access to your account" section.

Click the draw.io entry.

Click the "REMOVE ACCESS" button.

Note that draw.io has been tested extensively for security, including passing Google's security audit for internal usage with Google Drive in 2018. If your IT administrator has security concerns, please direct them at support@draw.io and we can discuss them in detail.