GSTR3B Return for Feb 202

A user filed their GSTR 3B for February 2020 and realised they declared less GST liability than in their GSTR 1. They are seeking guidance on whether they can file a rectification or amendment return for that month. The advice given is that the additional liability can be disclosed in the following month's (March) GSTR 3B, but interest at 18% per annum will be applicable for the one-month delay.