That is not a module it is part of virtuemart product setup. Please see below navigation to find related products.
1- Joomla Admin > Components > Virtuemart > Products
2- Select your product from list.
3- On the right choose Custom Fields , now you will see related categories and related products. Simply enter the name of the product and you will get popup display with matching product names, simply click on them and they will be added in the list.
See you around...