Pop up input binding window when creating trigger

code show as below:

Then when I run the create trigger statement a window pops up as follows

My direct application 

Then a tuple is inserted into the student table. In theory, his student number is assigned by the system and the value is 2010341001

But the screen shows like this

I typed the code according to the book, so I think it must be the window that popped up just now that some operations are required to assign Liu Hui's student number to 2010341001