The format for entering the codes is:
QTY,ASSEMBLYCODE;QTY,ASSEMBLYCODE
So in your case you would enter for Panel 1:
2,PART_A;1,PART_B;5,PART_C
For Panel 2 you would enter:
3,PART_A;1,PART_B;7,PART_C
A quantity of 1 is the default, so in either case for PART_B which has a quantity of 1, you would not need to enter the 1, before the assemblycode, so the format could be:
2,PART_A;PART_B;5,PART_C
Good luck!