wrong GST payment

Emerson.C (Asst., Manager) (218 Points)

01 March 2019  
My client has filed gst return for both GST 3b and GSTR 1 with excess value in Dec'18 and GST 18% tax payment adjsuted with input tax and need to adjust thee difference in next month returns and have to pay in 12% slab in 3B return so how to adjust and file the return.