fresh invoice of Gst

hi everyone ! one of my friend is working in a xyz co. A service was provided to his company in August on which appropriate amount gst was also charged on the bill value but he forgot to book the bill until now. Both his company and supplier of service have already filed their respective gst return for the said month. What remedies does he has right now so that his bill could also be booked and party payment could also be settled and appropriate amount of itc could also be taken. pls provide ur suggestions quickly.