How to Define the Lot Control Item when Item Has Transactions Onhand Qty Zero

 Dear Team

We define item, without lot control and these items have transactions. Know due to bussiness need we need to have these item as lot control

I did the following;

Issue the onhand qty

Update the Item template with lot control attribute

while trying to enbale to lot attribute, org level, system is not allowing, lot attibute is dimmed.

need your expert advice.

regards/Imtiyaz