To register WhatsApp Business API, you can use your current WhatsApp or WhatsApp Business number, but you have to delete the previous account that has been registered.
It is highly recommended to register WhatsApp Business API with a number that has never been registered for WhatsApp or WhatsApp Business.
Once the number is registered to a WhatsApp Business API, it cannot be downgraded, but it can be migrated from a WABAID to another.
If you want to use WhatsApp and WhatsApp Business, you must obtain a new phone number.
For more detailed information, you can refer to these link https://developers.facebook.com/docs/whatsapp/guides/phone-number/