Yes, the admin or the store owner can assign store products to the seller/vendors/partners by going to the Admin Panel and following the path Marketplace > Partners > Edit any Partner > Payment & Commission tab > Add Products. The admin can enter the name of the store products which he wants to assign to that particular seller/vendor/partner.
Note- The admin can only add store products and not other seller’s products to any seller. Suppose there is a product A and there are two sellers S1 and S2 then the admin can assign Product A to either Seller S1 or to the Seller S2. If the admin wants to assign products to the multiple sellers then you can check this module- Opencart Marketplace Price Comparision.