How I can stop the flow from updating the opportunity owner until the request has been approved?

I've got a flow called from an action button on the opportunity object. The flow allows the user to request that the opportunity owner be changed to another user whom.they specify on a screen which appears when they press the button on the opportunity. The last part of my flow is a 'submit for approval' action. However I'm finding that although the flow successfully invokes the approval process, it is still changing the opportunity owner before the approval request has actually been approved. Any ideas why this might be and how I can stop the flow from updating the opportunity owner until the request has been approved? Thanks!