Another (easier) way to identify:
1. Make sure each circuit has a load plugged into it and turned “on”.
2. Turn off all breakers.
3. Disconnect 1 neutral wire in the panel.
4. Systematically turn breakers on/off until you measure 120v between the disconnected neutral wire and anything grounded (e.g. the panel, neutral bus, etc). The breaker you turned to get 120V on the neutral wire corresponds with that neutral wire.
This works because there is no current flowing in the circuit with the disconnected neutral, thus no voltage drop across the load, thus the whole “circuit”, including the disconnected neutral wire is at 120V.