This video covers the basic steps. https://www.youtube.com/watch?v=KviaJ_Cqt6I
1. Install the non drive side cup until it's fully tight. Set the inner bearing flush with the end of the cup. You’ll tighten that up last. Add some grease to the bearing BB axle contact point. That will help keep water from getting into the BB.
2. It’s critical that the chainring spider collar is seated to the torque sensor. There’s a notch that it indexes to. If it’s not seated the chainring spider will spin freely without engaging the sensor. Be careful when installing the sensor into the BB that it doesn’t come unseated. If it does come unseated you can zap strap the chainring spider to the chainstay to remove the lock ring. Otherwise the spider will just spin while you’re trying to loosen it.
3. Feed the torque sensor cable through the BB shell into the frame. Carefully feed the torque sensor body into the frame. There are notches into the non drive side cup that the sensor seats into. They prevent the sensor from spinning while tightening the drive side cup.
4. Install and fully tighten the drive side cup. Install the chainring/spider to the collar. Install and tighten the spider look ring. There’s arrows printed on it indicating the direction.
5. Lightly tighten the non drive side bearing in the cup. Do not fully tighten. Back it off a slight turn once there’s resistance. You don’t want to put any lateral load on the bearing.
6. Install the crack arms and you’re done.
Avoid spraying water near the downtube/battery and seat post. Water can get into the bottom bracket through the downtube and seat tube.
Do not loosen or tighten the non drive side cup once the torque sensor is installed. That will spin the sensor in the BB and tear the cable. Remove the drive side cup and completely remove the sensor before tightening/loosening the non drive side cup.