I would like to know how to put this refrigerator into test mode please.

Hello
To check stored error codes within 3 hours after the error : Press the Ice Plus button and Freezer button simultaneously 3 hours after the error : All errors, except for “Er rt”, “Er SS”, “Er IS”, “Er gF”, “Er It”, “Er HS”.
“Er IS(except for Icing sensor)”, “Er gF”, “Er It” error, are displayed. “Er IS” which is displayed without input of user is the error of Icing Sensor. Also see the complete diagnostic guide link below. Matt Ace technician