Cancellation of provisional registration

Persons Registered under VAT/Service Tax Laws Not liable to Register Under GST

Any  person registered under any of the existing laws, who is not liable to be registered under the Act can opt to cancel the registration granted to him. He must submit an application electronically in FORM GST REG-29 at the Common Portal .

I am trying to find where to file REG-29 to cancel my provisional registration since my turnover is less Rs. 20 lakh. I have migrated to GST because I was liable to Service tax. Please advise.