Have a look here ...
Hal Leonard Guitar Method Book (Left-handed edition...)...
... This will get you on the right track; it's very good.
Here's another on the subject, but I've not looked into it very deeply; probably worth the minimal expense occasioned...
How to Play the left-handed Guitar ...
Another, based more on the electric guitar (although the ideas are the same for any guitar...)...
Left-handed Guitar Method ...
I usually buy books and methods of the sort second-hand, as they are almost always in 'new' condition, but cost far less. It would be a Good Idea to buy all three, second-hand, in my opinion, as there is always something to learn from all of these methods. The cost is very low.
Have a look at these; if questions still remain, get back to us on here. Hope this helps
Douglas