No easy way but the system pulls based on when you make the trip.
Whichever trip was booked first, not date of trip, would have pulled banked points that were that way when booking. So if the points were all banked before the first reservation was made, that is the one that will have all the banked points.
If you banked some after one trip was made, then it would have banked points in the second one.
To double check, you can go to the points activity statement to see how they were pulled.
Or, go to one of the trips, modify it but don’t change a things, and rebook at the end. You will see a points summary there and it will show what was used!