you can add/less your disput to your next month gstr 3b
example - your real sale of december is sgts 500 and cgst 500 and you show in dec 3b 250cgst 250 sgst ... in this case in gstr 3b jan month total sgst sales tax of jan-250 (outward supply) total cgst sales tax of jan - 250
sorry where i show sgst sales tax of jan after it minus( -) that is plus (+) .. typing mistake sorry ... above example you have to add your liability to next month