You can only change the UoM on the Master Part, that is true.

But that can only be accomplished when the part doesn’t exist elsewhere as an engineering part or an inventory part. It has to be caught early in the process, if you’ve already used the part on orders or have connected it to other parts, you can’t change it.  In some narrow cases before use, you can delete the part from all other locations, so only the Master Part remains, but that is rare. I usually tell the engineers to be more precise the next time and make a new part with the right UoM, it is simpler and quicker.  

Thanks, @ShawnBerk  for your piece of advice..!!

Hi @ShawnBerk 

This part has no any transaction history.

No product structure.

No On hand stock

No Purchase orders and customer orders.

Inventory part exists

Purchase part exists

Supplier for purchase part exists

in this situation can we change the UOM in mater part.

@Deepak 

Yes, it is possible to change the UoM, but you’ll first have to delete the SfPP record, then the Purchase Part, then the Inventory Part in that order.  Then you should be able to make the change.  After that, the parts would need to be created again to pick up the new UoM information as it is derived from the Master Part on creation.