Hello Fenton,
It will be not quite convenient to add existing bookings to the Hotel Booking, however, still possible.
You will need to add new bookings under Bookings ->All Bookings ->New Booking filling in the Customer data (if required). You will be able to add any amount as a payment for the booking, so it will already be considered as paid. Once the booking is added, it will automatically be confirmed and you will be able to send a payment request to have the remaining balance due paid by the Customer.
Regards,
Andre