Section 40(1)(b) in Kerala Goods and Services Tax Rules, 2017
(b)the registered person shall within a period of thirty days from the date of his becoming eligible to avail the input tax credit under sub-section (1) of section 18 shall make a declaration, electronically, on the common portal in FORM GST ITC-01 to the effect that he is eligible to avail the input tax credit as aforesaid;