UOM not editable - Parts Requirement

Hi Team,

We have an issue while requesting the Parts from the parts screen, normally we add the required part and mentioned the Quantity and generate the ISO against some source organization. However please advice how we can change the UOM of the Part while requesting the Part. Attached the screen shot from the Parts screen please review.

Business Requirement

Real Scenario: Technician bought various shades of Paints and from which he need to create the final paint code so for this he need some ltr or ml quantity from those shades to make the final paint. For e.g.