A person registered under existing law (Central Excise/Service Tax/VAT) and who has been granted registration on a provisional basis wants to opt for composition scheme. How and when can he do that

Such a person has to electronically file a duly signed/verified intimation in FORM GST CMP-01, on the common portal, prior to 22nd June, 2017 or such further period as may be allowed by the Commissioner.

(FAQ 15: COMPOSITION LEVY)