Help!! Dexcom and new iPhone issue

Hi
I've got a new iPhone and have set everything up.

But i can't get my G5 dex transmitter to pair with the new phone. It says "transmitter not found" after I've scanned the barcode and waited the 30 mins.

It still appears to be reading fine on the old phone.

I've been on hold to dexcom uk for over an hour!!!!

Do i need to disconnect from the old phone first?

Do i stop the sensor first to do this???

HELP!!!

Thanks
Donna

Finally got through. Had to take everything off older phone first.