How to add a variation to a product

How do you add a variation to a product that has been selling for 6 months and now I want to add a new variation to that?
What would be the process to create the new variation listing so that it appears together on the page with the old product as a variation ?

Answer: It can be down via a flat flat file. You need to fill in all the details and upload it and wait 15/20mins and it should work. Is a bit tricky but once you know how to do it you’ll get the hang of it.