Suggestion:
System has the facility to define free offers for multiple products. This menu exists in SCM->SCM setting-> Promotions->Free Offers for Multiple Products.
Users can define offers for particular customers and sites. Users have to set the effective from and to dates. Then users have to set the chargeable quantity and free qty. After that, the user can click next to select the item. System will reflect all Product lists. Users can select the item/product for this offer. The user then can sort the already selected offer defined product as well as have the facility to remove this product from offer if required.
Please see the below screenshot for reference.