Embedded Signup can be set up to let business customers use their current WhatsApp Business app account and phone number during onboarding. Once successfully registered through this option, customers can use your app for large-scale messaging while still maintaining the ability to send individual messages via the WhatsApp Business app. Message history stays synchronized between both applications.
You can refer this meta doc on how to configure this - https://developers.facebook.com/docs/whatsapp/embedded-signup/custom-flows/onboarding-business-app-users/