Procedure to unclaimed gst

Mangal Singh Khinchi (Kota) (259 Points)

19 October 2017  
Sir, We are security service provider previously we are in RCM.but in GST RCM is not applicable to us.Some invoice which were related to Jan,Feb,Mar 2017.whose payment received to us on Sep & Oct 2017(Including GST).I am unable to understand how to met out this liability & what is the accounting treatment for GST we have received.