Update lookup field based on value selected on a subgrid

Hi,

We have a subgrid on the form which is called products, here we can select products(eg: ABC, XYZ). There is another lookup field on the form with value Yes/No. My requirement is if selected product is ABC then the lookup value should automatically be Yes and if selected product is XYZ then the lookup field value should be No. How can i accomplish this ?

Thanks