@kruthika pleas check @ShawnBerk ‘s answer from below post. The same would be applicable for your case:

Dear @kruthika 

try to change it here:

Hello,

We can edit UoM from Part master, but it doesnt reflect in Inventory Part and in the Inventory Part we can see the old UoM.

Is their any other solution ??

Regards,

Kruthika

@Marcel.Ausan did attach a previous post that will answer your question.

Hello,

Yes, i saw Marcel.Ausan answer 

But the Inventory Part is already Used in Purchase Requisition and Purchase Order , we cannot delete the Inventory Part and create new.

Marcel.Ausan

Regards, Kruthika

In my opinion, you aren't able to get around this other than creating a new master/inventory part.

Its always beneficial to double/triple check parts before any transactions take place, have seen customers implementing approval routes prior to a part being activated.

Is their any other solution ??

No, once used as described in the other post, it is not possible to change under any method.