Either when opening the transcription the first time, or when you click "Edit labels" in the menu, you will see the popup where you can edit the labels applied to the participants.

In this popup you can change two things:

When applying labels, you have the option to listen to a 5-second clip of the recording, where the AI have detected the given participant. To be sure of who it is, you can press the "Shuffle"-button, get a new random 5-second clip of the recording.