Refund of accumulated itc for april 2018 to march 2019

Resp Sir.  A  GST registered person OF Rajasthan applied for refund from Accumulated ITC .(PERIOD FROM APRIL2018 To March 2019) on 28/01/2021. Can  whole period s refund admisable? Which months ITC admisable and Which Months Accumulated ITC not admisable for  refund pertaining to taxpayer application date of refund ie 28/01/2021. Kindly reply with rules/ Section/ Notification.Thanks.

Only admissable for Jan to march.

Refer section 54

Thanks for yours valuable advise.