Cancellation of GST REGISTRATION

One of my friend continuing a restaurant business has taken Gst registration as a normal taxpayer with quarterly return with 5% Gst with no Itc in the month of July, '19 assuming that the yearly turnover will go more than 20 lakh. But now they found that the yearly turnover cannot possible more than 20 lakh as per present circumstances and now they want to cancel the Gst registration. Can anyone please guide how can they cancel the registration and what will be the process.