Chess (human vs player) edition

I had someone who did the project for me. The project was to create a chess program in Java. The program does not have a feature: if user selects a piece but then changes mind and wants to select another piece he cannot do that. so i want someone to do that for me. hope it is not too arduous. Also, I do not know if the program has checkmate (if it has good) but if don't please add that. I want someone to make a state diagram for it too. And explain me the work and tell me what algorithms have been used (Minimax, alpha beta, negamax) and which evaluation functions. There will be more simple questions regarding project but wont require you to do the coding for it just simple answering.