There's no way to transfer an app that is live on the App Store between iTunes Connect accounts. You'll have to remove the app from sale, upload it separately to the other iTunes Connect account and submit it as it was a new application.
The problems here are that users of the app that downloaded it originally will get no notification that it was removed or that it has been uploaded under a new account. So effectively you'll be leaving your entire user base behind and starting fresh.
Without some marketing, your users won't know that the app has moved. The app will also lose any reviews/ratings it has (good or bad).