That "N" is always the first value in the field due to being auto-entered isn't it?
If so, you can show all records and then use Replace field contents with the calculation option using an expression similar to:
Let ( L = RightValues ( YourField ; ValueCount ( YourField ) - 1 ) ;
Middle ( L ; Length ( L ) - 1 )
RightValues leaves a return at the end of the text it returns. That's probably harmless in your check box field, but to be on the safe side, I used the middle function to remove it.
Hmmm, that probably won't work unless you can perform a find to find only the records that have that N first....