Cannot pair my new Charge HR to my iPhone 6s

[TKW]

I have just purchased a Charge HR (my previous Charge stopped holding it's 'charge' so has been replaced). I have fully charged it and have gone to my account on my phone and tried to 'set up a device'. I press Charge HR then a pink screen comes up with 'Set up yout Fitbit Charge HR' at the bottom which I click on then it just says 'Loading...' and doesn't do anything else.
I have reset the tracker, the softwear is version36. I have rebooted my phone, I have checked there is no app update outstanding and rebooted my phone again, inc turning Bluetooth off and on again......
I have my old Flex attached to my phone as well which I have been using since the Charge kept failing.....
If I delete the app on my phone and reinstall, it says If I delete the app it will delete all its data as well - I don't wish to loose my history!
Any other suggestions please?
Thank you.

[MaginB]

It's great to see that you've visited the Fitbit Community @TKW! 

Try going to your bluetooth settings and tap on forget device, then try doing the setup again and if you still unable try doing the setup with a computer it the inconvenience persists I recommend contacting the Support Team so they can review your options. 

Hope it helps!