In order to convert MX products do Variable please follow the steps below:
1. & 2. Open Products -> All Products
3. Choose Semi Custom in Categories list
4. Choose Simple product in Product Types list
5. Click Filter button
6. Click Edit under the first product in the list
7. Note the initial product price
8. Choose Variable Product in the list
9. Click Attributes section
10. Choose Product Type in the list
11. Click the Add button
12. Click Select All button and make sure the two attributes appear in the field above
13. Click Used for Variations
14. Click Save Attributes
15. Click Variations section
16. Choose Create variations from all attributes from the list
17. Click the Go button and click OK for the next confirmations (not in the picture)
18. Choose Full Kit from the list
19. Click Expand link
20. Type in the price observed at step 7
21. Type in the price for the Backgrounds Only
22. Click Save Changes
23. Click Update to save the whole product
That is all for one product. Repeat the steps for each product in the list.