help attach 2 relation manager into a pivot table

so i have a GameProductCategoriesRelationManager and GameProductsRelationManager which is both related to GameResource i have a pivot table called 'game_product_category_pivot' i want to be able to attach products on my category via action for example 1. i click attach on row 1 2. the select box should show all the products related to the game 3. once save, row 1 id and all the products selected should be save on game_product_category_pivot