For easy understanding let's consider an example pgn file
So, My approach is that, when a pgn file is given it would be easy if we parse through out the file. Like for every step or every movement, we will also move that piece virtually(i mean the code should be that way). We should write the code such way that when there is a movement in on the board by the person it should also work simultaneously in the code. Then we can get the final positions easily after all the movements are done.