Page 79 of the pdf manual:
"changing the open/closed mode
1. Press MAN.
2. Press FUNC then e or d to select the channel storage bank.
3. Press FUNC then ./DELAY. Bank OPEN. or Bank CLOSED.
appears. After that message disappears, the fifteenth
digit on the second line of the display changes from + to
– or vice versa.
4. Repeat Steps 2 and 3 for each bank."