GST Default Notice for GSTR 3B of Jan. 2021

I have been identified as a QRMP taxpayer by GST Portal for the month of Jan. 2021 to March 2021. Further, I have no output tax liability for the month of Jan. 2021 because my input is greater than my output liability. Therefore, I have not paid any tax till 25th of Feb. 2021 for the month of Jan. 2021 being a QRMP taxpayer.
Now, I received mail from department regarding “Notice to return defaulter u/s 46 for not filing return”. The main Content of notice is as below –
Tax Period – JANUARY-2021 Type of Return – GSTR-3B
1. Being a registered taxpayer, you are required to furnish return for the supplies made or received and to discharge resultant tax liability for the aforesaid tax period by due date. It has been noticed that you have not filed the said return till date.
2. You are, therefore, requested to furnish the said return within 15 days failing which the tax liability will be assessed u/s 62 of the Act, based on the relevant material available with this office. Please note that in addition to tax so assessed, you will also be liable to pay interest and penalty as per provisions of the Act.

What should I do?