Can't connect HRM-PRO to Forerunner 745 using Bluetooth, only ANT+

I misplaced my HRM-PRO, so I had to buy a new one. The old one was connected to my Forerunner 745 using Bluetooth, but I'm not able to connect my new sensor using anything but ANT+. The reason I cant' use ANT+ is that it produces much worse HRV data than Bluetooth.

When I pair the sensor with the watch, I never get the choice to use Bluetooth.

How to I connect a HRM-PRO v 8.9 to a Forerunner 745 v 13.00 using Bluetooth (BLE)?