How to edit 2nd mobile version theme

Ok I hope this makes sense and the right section. Im not very advanced with wordpress but trying to learn more. I have a website and it has a great desktop theme ( I didnt set it up). Problem is it dosen’t look good on mobile at all. I am using wptouch free version right now, but not loving the look. I want to use anymobile theme switcher to use a completely different mobile theme. For the life of me I can not figure how you go about setting up and editing a 2nd theme without deactivating my main theme and messing the whole site up. Basically how do I work on a mobile theme, get it setup to be used with anymobile theme switcher without messing with the main desktop version. SOrry if this is a newb question. Even a link to a guide would be awesome. Thanks for your help!