How to set the original track selected by the singer to "No default voice"

Lounge / 大厅 / ラウンジ
1

As per the title, can I change the track where the singer has already been selected to “No default voice”? I’m really curious.

2

In the voice panel select (not set), I don’t know why it can’t be done also in the track
voice

「いいね！」 2
3

Thank you so much!