Input tax credit claiming for march

Only Input Credit for the month March 21 can be availed before the due date of September 21 Month's return.

No. ITC claim of the previous financial year was allowed only if the September return is filed on or before the due date. GSTR 3B is explained very lucidly in this article. https://bit.ly/2vRQclx. and this article about ITC will solve all the doubts regarding ITC - https://irisgst.com/all-about-input-tax-credit-itc-how-to-claim-input-tax-credit/