You need to separate the two issues. They are independent.
Your first task is to get reliable rpm readings.
What have you tried to get the IR sensor to work with the spinning tube? What issues do you see?
If the IR sensor can not be made to work with a spinning tube, perhaps you can mount a small magnet and use a hall sensor.
You will need to do some research on the bluetooth side of things to determine the protocol used by Zwift or an alternative.
Be aware, that you may need to use BLE (Bluetooth Low Energy).
Using an Arduino to measure and then transmit rpm data is a common project. The specifics of the measurement and the bluetooth need to be better defined.