how to get the "perosnalize" button in some available model

hello everyone.
i jus recently uploaded some of my work here:
https://www.shapeways.com/shops/jimmynar
and some people ask me and suggest me to personalize some of my cases, to add personal text
and something like that. my question is ¿how i can put the "personalize" button on an existing model
or how does it work?

Check out this tutorial.
https://www.shapeways.com/Co-Creator_Platform/How_to_join

thanks

Thanks! I needed this tutorial too!