Child product not showing as selected in product details page dropdown

[Nagaraj]

Hi ,

I have migrated virtuemart from version 2 to 3. I have several custom fields and child products to my products.
In the product detail page, there is a drop-down with child products showing in the drop-down. When i have selected the child product from the drop-down, page is showing the content from the selected product but in the drop-down it is not showing as select product. How can i change to make the product selected for drop-down.

Example :
HM-regular is main product
hm-alternate is child product of "HM-regular" shown in drop-down
when hm-alternate is selected, all information regarding child product is displaying properly but not showing as selected.

Thanks in advance