Just in case anyone else has the same question later, here is the process:
Either make an appointment at an Apple Stire or approved Service Provider for assessment of the broken device. They will then create a Repair ID, and forward it on to Apple.
Or, if like me you are too far from an Apple Store or authorised Sercive Provider, phone Apple Support and request a repair request to be generated. Apple Support will give you the info to be able to post the device in to them, check it over then let you know how much it will cost to repair.
In this case, as multiple things are wrong (screen and battery), the maximum cost will be AUD $701.95 in 1019 for a replacement (refurbished) iPhone 6s if not deemed repairable by the Tech. This is a lot more expensive than just the screen repair, and battery repair ordered separately, but there is no guarantee that the phone may not be determined to be unfixable anyway requiring a replacement.
A new iPhone 7 is currently AUD $749 for the 32GB model meaning that there is not much point in repairing the 6s...