If you want to merge two products into one (e.g. you want to customize one product with two different designs), it's very simple:
- You must first create the two products by selecting for each one the colors related to the visual (e.g. a white pattern for the dark colors t-shirts and a black pattern for the light colors t-shirts)
- You then go to your list of created products
Make sure that your two products to be merged are not published on your site.
- Choose the first product, click on "Options" and then on "Merge".
- Your second product will appear in the list of compatible products on the right of the screen
- Once selected, click on "Merge with secondary product".
That's it, the product is now merged.
You'll then be redirected to your products and you'll see that the secondary product can no longer be published on your site, but you can still edit it to modify it.