1. Entering to your webstore [Back Office] and [Login].

2. Go to Left [Menu] -> [Catalog] -> [Products].

3. Click [Product] you would like to edit and.

4. Click Tab 4 - [Association].

4.1. Key-in product you would like to display in [Related Product].

4.2. Multiple related product is allow.

4.3. Click [Save and Stay] to save action above and stay same page.